2023 WST Classic

The tournament featured 128 players. The top 64 players in the snooker world rankings after the Players Championship were seeded in the draw, with the remaining 64 players drawn at random against them. Matches were played as the best of seven {{cuegloss|frame|frames}} up to and including the quarter-finals. The semi-finals were played over the best of nine frames. The final was played over the best of 11 frames. The last three rounds were all played on the final day.

The event featured a prize fund of £427,000, with the winner receiving £80,000. The breakdown of prize money for this event is shown below:{{Cite web |title=One More Lap in Race to Hull |url=https://wst.tv/one-more-leg-in-race-to-hull/ |archive-url=https://web.archive.org/web/20230303003730/https://wst.tv/one-more-leg-in-race-to-hull/ |url-status=dead |archive-date=March 3, 2023 |access-date=2023-03-03 |website=World Snooker Tour |language=en-UK}}

{{div col}}

• Winner: £80,000
• Runner-up: £35,000
• Semi-final: £17,500
• Quarter-final: £11,000
• Last 16: £7,500
• Last 32: £4,500
• Last 64: £3,000
• Highest break: £5,000
• Total: £427,000

{{div col end}}

{{#invoke:RoundN|main|columns=4

|team-width=220

|short_brackets=yes

|bold_winner=high

|RD1 = Last 128
Best of 7 frames|RD2 = Last 64
Best of 7 frames | RD3 = Last 32
Best of 7 frames |3rdplace=no| RD4=Last 16
Best of 7 frames

|| {{flagathlete|Ronnie O'Sullivan|ENG}} (1)|4 |{{flagathlete|Mohamed Ibrahim|EGY}}|2

|| {{flagathlete|David Grace|ENG}} (64)|4 |{{flagathlete|Ryan Thomerson|AUS}}|1

|| {{flagathlete|Sam Craigie|ENG}} (32)|2 |{{flagathlete|Hammad Miah|ENG}}|4

|| {{flagathlete|Jamie Jones|WAL}} (33)|4 |{{flagathlete|Rory McLeod|JAM}}|2

|| {{flagathlete|Gary Wilson|ENG}} (16)|4 |{{flagathlete|Lei Peifan|CHN}}|0

|| {{flagathlete|Yuan Sijun|CHN}} (49)|4 |{{flagathlete|Andy Lee|HKG}}|0

|| {{flagathlete|Ryan Day|WAL}} (17)|1 |{{flagathlete|Steven Hallworth|ENG}}|4

|| {{flagathlete|Cao Yupeng|CHN}} (48)|4 |{{flagathlete|Craig Steadman|ENG}}|3

|| {{flagicon|ENG}} Ronnie O'Sullivan (1){{efn|O'Sullivan withdrew because of an elbow injury.{{Cite web |last= |date=2023-03-19 |title=O'Sullivan Pulls Out Of WST Classic |url=https://wst.tv/osullivan-pulls-out-of-wst-classic/ |archive-url=https://web.archive.org/web/20230319181308/https://wst.tv/osullivan-pulls-out-of-wst-classic/ |url-status=dead |archive-date=March 19, 2023 |access-date=2023-03-19 |website=World Snooker |language=en-US}}https://twitter.com/ronnieo147/status/1637449208826404864}}|w/d |{{flagicon|ENG}} David Grace (64)|w/o

|| {{flagicon|ENG}} Hammad Miah|3 |{{flagicon|WAL}} Jamie Jones (33)|4

|| {{flagicon|ENG}} Gary Wilson (16)|4 |{{flagicon|CHN}} Yuan Sijun (49)|3

|| {{flagicon|ENG}} Steven Hallworth|2 |{{flagicon|CHN}} Cao Yupeng (48)|4

|| {{flagicon|ENG}} David Grace (64)|4 |{{flagicon|WAL}} Jamie Jones (33)|2

|| {{flagicon|ENG}} Gary Wilson (16)|4 |{{flagicon|CHN}} Cao Yupeng (48)|3

|| {{flagicon|ENG}} David Grace (64)|1 |{{flagicon|ENG}} Gary Wilson (16)|4

}}

{{#invoke:RoundN|main|columns=4

|team-width=220

|short_brackets=yes

|bold_winner=high

|RD1 = Last 128
Best of 7 frames | RD2 = Last 64
Best of 7 frames | RD3 = Last 32
Best of 7 frames |3rdplace=no| RD4=Last 16
Best of 7 frames

|| {{flagathlete|Jordan Brown|NIR}} (41)|1 |{{flagathlete|Allan Taylor|ENG}}|4

|| {{flagathlete|Jimmy Robertson|ENG}} (24)|3 |{{flagathlete|Lukas Kleckers|GER}}|4

|| {{flagathlete|Elliot Slessor|ENG}} (56)|4 |{{flagathlete|Himanshu Jain|IND}}|0

|| {{flagathlete|Luca Brecel|BEL}} (9)|2 |{{flagathlete|Haydon Pinhey|ENG}}|4

|| {{flagathlete|Liam Highfield|ENG}} (40)|4 |{{flagathlete|Marco Fu|HKG}}|1

|| {{flagathlete|Zhou Yuelong|CHN}} (25)|4 |{{flagathlete|Julien Leclercq|BEL}}|3

|| {{flagathlete|Jackson Page|WAL}} (57)|4 |{{flagathlete|Anton Kazakov|UKR}}|3

|| {{flagathlete|Mark Williams|WAL}} (8)|4 |{{flagathlete|Sean O'Sullivan|ENG}}|3

|| {{flagicon|ENG}} Allan Taylor|0 |{{flagicon|GER}} Lukas Kleckers|4

|| {{flagicon|ENG}} Elliot Slessor (56)|1 |{{flagicon|ENG}} Haydon Pinhey|4

|| {{flagicon|ENG}} Liam Highfield (40)|2 |{{flagicon|CHN}} Zhou Yuelong (25)|4

|| {{flagicon|WAL}} Jackson Page (57)|4 |{{flagicon|WAL}} Mark Williams (8)|3

|| {{flagicon|GER}} Lukas Kleckers|4 |{{flagicon|ENG}} Haydon Pinhey|2

|| {{flagicon|CHN}} Zhou Yuelong (25)|2 |{{flagicon|WAL}} Jackson Page (57)|4

|| {{flagicon|GER}} Lukas Kleckers|4 |{{flagicon|WAL}} Jackson Page (57)|0

}}

{{#invoke:RoundN|main|columns=4

|team-width=220

|short_brackets=yes

|bold_winner=high

|RD1 = Last 128
Best of 7 frames|RD2 = Last 64
Best of 7 frames | RD3 = Last 32
Best of 7 frames |3rdplace=no| RD4=Last 16
Best of 7 frames

|| {{flagathlete|Judd Trump|ENG}} (5)|4 |{{flagathlete|David Lilley|ENG}}|1

|| {{flagathlete|Wu Yize|CHN}} (60)|4 |{{flagathlete|Ashley Hugill|ENG}}|1

|| {{flagathlete|Joe Perry|ENG}} (28)|4 |{{flagathlete|Duane Jones|WAL}}|0

|| {{flagathlete|Graeme Dott|SCO}} (37)|2 |{{flagathlete|Jimmy White|ENG}}|4

|| {{flagathlete|Jack Lisowski|ENG}} (12)|4 |{{flagathlete|Louis Heathcote|ENG}}|3

|| {{flagathlete|Dominic Dale|WAL}} (53)|2 |{{flagathlete|Si Jiahui|CHN}}|4

|| {{flagathlete|Ricky Walden|ENG}} (21)|1 |{{flagathlete|Ben Mertens|BEL}}|4

|| {{flagathlete|Pang Junxu|CHN}} (44)|4 |{{flagathlete|Jenson Kendrick|ENG}}|2

|| {{flagicon|ENG}} Judd Trump (5)|4 |{{flagicon|CHN}} Wu Yize (60)|1

|| {{flagicon|ENG}} Joe Perry (28)|3 |{{flagicon|ENG}} Jimmy White|4

|| {{flagicon|ENG}} Jack Lisowski (12)|2 |{{flagicon|CHN}} Si Jiahui|4

|| {{flagicon|BEL}} Ben Mertens|0 |{{flagicon|CHN}} Pang Junxu (44)|4

|| {{flagicon|ENG}} Judd Trump (5)|2 |{{flagicon|ENG}} Jimmy White|4

|| {{flagicon|CHN}} Si Jiahui|0 |{{flagicon|CHN}} Pang Junxu (44)|4

|| {{flagicon|ENG}} Jimmy White|1 |{{flagicon|CHN}} Pang Junxu (44)|4

}}

{{#invoke:RoundN|main|columns=4

|team-width=220

|short_brackets=yes

|bold_winner=high

|RD1 = Last 128
Best of 7 frames|RD2 = Last 64
Best of 7 frames | RD3 = Last 32
Best of 7 frames |3rdplace=no| RD4=Last 16
Best of 7 frames

|| {{flagathlete|Ben Woollaston|ENG}} (45)|4 |{{flagathlete|Dylan Emery|WAL}}|2

|| {{flagathlete|Hossein Vafaei|IRN}} (20)|4 |{{flagathlete|John Astley|ENG}}|2

|| {{flagathlete|Scott Donaldson|SCO}} (52)|4 |{{flagathlete|Zak Surety|ENG}}|2

|| {{flagathlete|Barry Hawkins|ENG}} (13)|4 |{{flagathlete|Barry Pinches|ENG}}|0

|| {{flagathlete|Lyu Haotian|CHN}} (36)|4 |{{flagathlete|Michael Judge|IRL}}|1

|| {{flagathlete|Joe O'Connor|ENG}} (29)|4 |{{flagathlete|Jamie O'Neill|ENG}}|1

|| {{flagathlete|Oliver Lines|ENG}} (61)|4 |{{flagathlete|Mitchell Mann|ENG}}|0

|| {{flagathlete|Neil Robertson|AUS}} (4)|4 |{{flagathlete|Luke Simmonds|ENG}}|2

|| {{flagicon|ENG}} Ben Woollaston (45)|1 |{{flagicon|IRN}} Hossein Vafaei (20)|4

|| {{flagicon|SCO}} Scott Donaldson (52)|4 |{{flagicon|ENG}} Barry Hawkins (13)|0

|| {{flagicon|CHN}} Lyu Haotian (36)|4 |{{flagicon|ENG}} Joe O'Connor (29)|1

|| {{flagicon|ENG}} Oliver Lines (61)|4 |{{flagicon|AUS}} Neil Robertson (4)|3

|| {{flagicon|IRN}} Hossein Vafaei (20)|2 |{{flagicon|SCO}} Scott Donaldson (52)|4

|| {{flagicon|CHN}} Lyu Haotian (36)|3 |{{flagicon|ENG}} Oliver Lines (61)|4

|| {{flagicon|SCO}} Scott Donaldson (52)|1 |{{flagicon|ENG}} Oliver Lines (61)|4

}}

{{#invoke:RoundN|main|columns=4

|team-width=220

|short_brackets=yes

|bold_winner=high

|RD1 = Last 128
Best of 7 frames|RD2 = Last 64
Best of 7 frames | RD3 = Last 32
Best of 7 frames |3rdplace=no| RD4=Last 16
Best of 7 frames

|| {{flagathlete|Mark Allen|NIR}} (3)|4 |{{flagathlete|Peter Lines|ENG}}|0

|| {{flagathlete|Mark Davis|ENG}} (62)|4 |{{flagathlete|Fergal O'Brien|IRL}}|2

|| {{flagathlete|Noppon Saengkham|THA}} (30)|4 |{{flagathlete|Ian Burns|ENG}}|3

|| {{flagathlete|Fan Zhengyi|CHN}} (35)|4 |{{flagathlete|Andres Petrov|EST}}|0

|| {{flagathlete|Stuart Bingham|ENG}} (14)|4 |{{flagathlete|Ng On-yee|HKG}}|0

|| {{flagathlete|Matthew Stevens|WAL}} (51)|4 |{{flagathlete|Victor Sarkis|BRA}}|1

|| {{flagathlete|Anthony McGill|SCO}} (19)|4 |{{flagathlete|Peng Yisong|CHN}}|0

|| {{flagathlete|Martin Gould|ENG}} (46)|4 |{{flagathlete|Andrew Higginson|ENG}}|2

|| {{flagicon|NIR}} Mark Allen (3)|4 |{{flagicon|ENG}} Mark Davis (62)|3

|| {{flagicon|THA}} Noppon Saengkham (30)|4 |{{flagicon|CHN}} Fan Zhengyi (35)|3

|| {{flagicon|ENG}} Stuart Bingham (14)|4 |{{flagicon|WAL}} Matthew Stevens (51)|2

|| {{flagicon|SCO}} Anthony McGill (19)|1 |{{flagicon|ENG}} Martin Gould (46)|4

|| {{flagicon|NIR}} Mark Allen (3)|1 |{{flagicon|THA}} Noppon Saengkham (30)|4

|| {{flagicon|ENG}} Stuart Bingham (14)|4 |{{flagicon|ENG}} Martin Gould (46)|1

|| {{flagicon|THA}} Noppon Saengkham (30)|2 |{{flagicon|ENG}} Stuart Bingham (14)|4

}}

{{#invoke:RoundN|main|columns=4

|team-width=220

|short_brackets=yes

|bold_winner=high

|RD1 = Last 128
Best of 7 frames|RD2 = Last 64
Best of 7 frames | RD3 = Last 32
Best of 7 frames |3rdplace=no| RD4=Last 16
Best of 7 frames

|| {{flagathlete|Thepchaiya Un-Nooh|THA}} (43)|4 |{{flagathlete|Asjad Iqbal|PAK}}|2

|| {{flagathlete|Ding Junhui|CHN}} (22)|3 |{{flagathlete|Xu Si|CHN}}|4

|| {{flagathlete|Mark King|ENG}} (54){{efn|King was suspended by the World Snooker Tour before his match.{{Cite web |last= |date=18 March 2023 |title=WPBSA Statement: Mark King |url=https://wst.tv/wpbsa-statement-mark-king/ |archive-url=https://web.archive.org/web/20230318144309/https://wst.tv/wpbsa%2Dstatement%2Dmark%2Dking/ |url-status=dead |archive-date=March 18, 2023 |access-date=22 March 2023 |website=World Snooker |language=en-US}}}}|w/d |{{flagathlete|Muhammad Asif|PAK}}|w/o

|| {{flagathlete|Ali Carter|ENG}} (11)|4 |{{flagathlete|Dechawat Poomjaeng|THA}}|1

|| {{flagathlete|Anthony Hamilton|ENG}} (38)|4 |{{flagathlete|Farakh Ajaib|PAK}}|3

|| {{flagathlete|Matthew Selt|ENG}} (27)|4 |{{flagathlete|Michael Holt|ENG}}|3

|| {{flagathlete|Andy Hicks|ENG}} (59)|1 |{{flagathlete|James Cahill|ENG}}|4

|| {{flagathlete|Shaun Murphy|ENG}} (6)|4 |{{flagathlete|Oliver Brown|ENG}}|0

|| {{flagicon|THA}} Thepchaiya Un-Nooh (43)|2 |{{flagicon|CHN}} Xu Si|4

|| {{flagicon|PAK}} Muhammad Asif|0 |{{flagicon|ENG}} Ali Carter (11)|4

|| {{flagicon|ENG}} Anthony Hamilton (38)|4 |{{flagicon|ENG}} Matthew Selt (27)|3

|| {{flagicon|ENG}} James Cahill|4 |{{flagicon|ENG}} Shaun Murphy (6)|3

|| {{flagicon|CHN}} Xu Si|2 |{{flagicon|ENG}} Ali Carter (11)|4

|| {{flagicon|ENG}} Anthony Hamilton (38)|2 |{{flagicon|ENG}} James Cahill|4

|| {{flagicon|ENG}} Ali Carter (11)|4 |{{flagicon|ENG}} James Cahill|3

}}

{{#invoke:RoundN|main|columns=4

|team-width=220

|short_brackets=yes

|bold_winner=high

|RD1 = Last 128
Best of 7 frames|RD2 = Last 64
Best of 7 frames | RD3 = Last 32
Best of 7 frames |3rdplace=no| RD4=Last 16
Best of 7 frames

|| {{flagathlete|Kyren Wilson|ENG}} (7)|4 |{{flagathlete|Dean Young|SCO}}|1

|| {{flagathlete|Stuart Carrington|ENG}} (58)|4 |{{flagathlete|Adam Duffy|ENG}}|1

|| {{flagathlete|Chris Wakelin|ENG}} (26)|4 |{{flagathlete|Reanne Evans|ENG}}|1

|| {{flagathlete|Tian Pengfei|CHN}} (39)|4 |{{flagathlete|Alfie Burden|ENG}}|3

|| {{flagathlete|John Higgins|SCO}} (10)|4 |{{flagathlete|Michael White|WAL}}|3

|| {{flagathlete|Mark Joyce|ENG}} (55)|4 |{{flagathlete|Gerard Greene|NIR}}|1

|| {{flagathlete|Tom Ford|ENG}} (23)|3 |{{flagathlete|Andrew Pagett|WAL}}|4

|| {{flagathlete|Jamie Clarke|WAL}} (42)|4 |{{flagathlete|Rebecca Kenna|ENG}}|0

|| {{flagicon|ENG}} Kyren Wilson (7)|4 |{{flagicon|ENG}} Stuart Carrington (58)|0

|| {{flagicon|ENG}} Chris Wakelin (26)|3 |{{flagicon|CHN}} Tian Pengfei (39)|4

|| {{flagicon|SCO}} John Higgins (10)|4 |{{flagicon|ENG}} Mark Joyce (55)|1

|| {{flagicon|WAL}} Andrew Pagett|2 |{{flagicon|WAL}} Jamie Clarke (42)|4

|| {{flagicon|ENG}} Kyren Wilson (7)|4 |{{flagicon|CHN}} Tian Pengfei (39)|0

|| {{flagicon|SCO}} John Higgins (10)|4 |{{flagicon|WAL}} Jamie Clarke (42)|0

|| {{flagicon|ENG}} Kyren Wilson (7)|2 |{{flagicon|SCO}} John Higgins (10)|4

}}

{{#invoke:RoundN|main|columns=4

|team-width=220

|short_brackets=yes

|bold_winner=high

|RD1 = Last 128
Best of 7 frames|RD2 = Last 64
Best of 7 frames | RD3 = Last 32
Best of 7 frames |3rdplace=no| RD4=Last 16
Best of 7 frames

|| {{flagathlete|Jak Jones|WAL}} (47)|4 |{{flagathlete|Sanderson Lam|ENG}}|1

|| {{flagathlete|David Gilbert|ENG}} (18)|4 |{{flagathlete|Ian Martin|ENG}}|0

|| {{flagathlete|Robbie Williams|ENG}} (50)|4 |{{flagathlete|Aaron Hill|IRL}}|1

|| {{flagathlete|Robert Milkins|ENG}} (15)|4 |{{flagathlete|Mink Nutcharut|THA}}|2

|| {{flagathlete|Stephen Maguire|SCO}} (34)|4 |{{flagathlete|Alexander Ursenbacher|SUI}}|3

|| {{flagathlete|Xiao Guodong|CHN}} (31)|3 |{{flagathlete|Daniel Wells|WAL}}|4

|| {{flagathlete|Zhang Anda|CHN}} (63)|4 |{{flagathlete|Peter Devlin|ENG}}|3

|| {{flagathlete|Mark Selby|ENG}} (2)|4 |{{flagathlete|Robbie McGuigan|NIR}}|1

|| {{flagicon|WAL}} Jak Jones (47)|2 |{{flagicon|ENG}} David Gilbert (18)|4

|| {{flagicon|ENG}} Robbie Williams (50)|4 |{{flagicon|ENG}} Robert Milkins (15)|2

|| {{flagicon|SCO}} Stephen Maguire (34)|1 |{{flagicon|WAL}} Daniel Wells|4

|| {{flagicon|CHN}} Zhang Anda (63)|3 |{{flagicon|ENG}} Mark Selby (2)|4

|| {{flagicon|ENG}} David Gilbert (18)|2 |{{flagicon|ENG}} Robbie Williams (50)|4

|| {{flagicon|WAL}} Daniel Wells|1 |{{flagicon|ENG}} Mark Selby (2)|4

|| {{flagicon|ENG}} Robbie Williams (50)|3 |{{flagicon|ENG}} Mark Selby (2)|4

}}

{{#invoke:RoundN|main|columns=3

|team-width=180

|short_brackets=yes

|bold_winner=high

|RD1 = Quarter-finals
Best of 7 frames|RD2 = Semi-finals
Best of 9 frames |3rdplace=no| RD3 = Final
Best of 11 frames

|| {{flagicon|ENG}} Gary Wilson (16)|4 |{{flagicon|GER}} Lukas Kleckers|1

|| {{flagicon|CHN}} Pang Junxu (44)|4 |{{flagicon|ENG}} Oliver Lines (61)|3

|| {{flagicon|ENG}} Stuart Bingham (14)|2 |{{flagicon|ENG}} Ali Carter (11)|4

|| {{flagicon|SCO}} John Higgins (10)|2 |{{flagicon|ENG}} Mark Selby (2)|4

|| {{flagicon|ENG}} Gary Wilson (16)|4 |{{flagicon|CHN}} Pang Junxu (44)|5

|| {{flagicon|ENG}} Ali Carter (11)|0 |{{flagicon|ENG}} Mark Selby (2)|5

|| {{flagicon|CHN}} Pang Junxu (44)|2 |{{flagicon|ENG}} Mark Selby (2)|6

}}

A total of 88 century breaks were made during the event.{{Cite web |title=Centuries – WST Classic 2023 |url=https://livescores.worldsnookerdata.com/Centuries/CenturyBreaks/14625/wst-classic-2023 |access-date=22 March 2023 |website=livescores.worldsnookerdata.com |archive-date=16 March 2023 |archive-url=https://web.archive.org/web/20230316195709/https://livescores.worldsnookerdata.com/Centuries/CenturyBreaks/14625/wst-classic-2023 |url-status=dead }}

{{div col}}

• 147, 115 {{ndash}} Thepchaiya Un-Nooh
• 143, 140 {{ndash}} Shaun Murphy
• 141, 123 {{ndash}} Daniel Wells
• 140 {{ndash}} Mark Joyce
• 139 {{ndash}} Pang Junxu
• 138, 138, 120, 105, 104 {{ndash}} Mark Selby
• 138, 130, 104 {{ndash}} Xu Si
• 137, 104 {{ndash}} Ronnie O'Sullivan
• 137 {{ndash}} Stephen Maguire
• 136, 135, 126, 126, 121, 102 {{ndash}} John Higgins
• 136 {{ndash}} Andrew Higginson
• 135, 135, 121, 107, 103 {{ndash}} Gary Wilson
• 135, 104, 103 {{ndash}} Hossein Vafaei
• 135 {{ndash}} Anthony McGill
• 133 {{ndash}} Ding Junhui
• 132 {{ndash}} Jimmy White
• 131, 113 {{ndash}} Judd Trump
• 131 {{ndash}} Jamie Jones
• 131 {{ndash}} Andrew Pagett
• 130 {{ndash}} Graeme Dott
• 129, 112 {{ndash}} Barry Hawkins
• 129, 106, 101 {{ndash}} Ali Carter
• 129, 101 {{ndash}} Jack Lisowski
• 128, 102, 102 {{ndash}} Zhou Yuelong
• 128 {{ndash}} John J. Astley
• 127 {{ndash}} Tom Ford
• 126 {{ndash}} Noppon Saengkham
• 123 {{ndash}} Si Jiahui
• 122 {{ndash}} Xiao Guodong
• 120, 118, 117 {{ndash}} Lyu Haotian
• 120 {{ndash}} David Grace
• 115, 113 {{ndash}} Haydon Pinhey
• 115, 103 {{ndash}} Chris Wakelin
• 113, 100 {{ndash}} David Gilbert
• 110 {{ndash}} Jackson Page
• 109, 100 {{ndash}} Stuart Bingham
• 109 {{ndash}} Lukas Kleckers
• 109 {{ndash}} Matthew Selt
• 107 {{ndash}} Anton Kazakov
• 107 {{ndash}} Ben Mertens
• 105, 101 {{ndash}} Kyren Wilson
• 105 {{ndash}} Jenson Kendrick
• 104, 103 {{ndash}} Jamie Clarke
• 104 {{ndash}} Anthony Hamilton
• 103, 100 {{ndash}} Neil Robertson
• 102 {{ndash}} Mark Davis
• 101 {{ndash}} James Cahill
• 101 {{ndash}} Dechawat Poomjaeng
• 100 {{ndash}} Fan Zhengyi
• 100 {{ndash}} Liam Highfield
• 100 {{ndash}} Yuan Sijun

{{div col end}}

{{reflist|group=n}}

{{notelist}}

{{reflist}}

{{2022–23 snooker season}}

WST Classic

WST Classic

WST Classic

Category:Snooker competitions in England

Category:Sport in Leicester