Petrov's Defence#Three Knights Game

White's two main choices for move three are 3.Nxe5 (the Classical Variation) and 3.d4 (the Steinitz Variation). 3.Nxe5 is more popular but they often lead to similar positions and "there is no clear reason to prefer one move over the other".Janjgava, p. 107

3.Nc3 may transpose to the Four Knights Game. 3.Bc4 may lead to the Boden–Kieseritzky Gambit or transpose to the Two Knights Defence. Occasionally seen is the {{chessgloss|quiet move|quiet}} 3.d3, the French Attack.

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| Position after 3.Nxe5 d6

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After 3.Nxe5, the Classical Variation, the standard reply for Black is 3...d6.

Most often, White follows the main line 3...d6 4.Nf3 Nxe4 5.d4 (5.Bd3{{chesspunc|!?}} is also playable, known as the Millennium Attack) d5 6.Bd3. This position is similar to an Exchange French in which Black has played the extra move ...Nf6-e4, however this extra move is not necessarily to Black's advantage. White will try to drive Black's advanced knight from e4 with moves like c4 and Re1. In practice White is usually able to achieve this, but at some structural cost such as having to play c4, which balances out.{{Citation |last=Burgess |first=Graham |author-link=Graham Burgess |title=The Mammoth Book of Chess |year=2010 |publisher=Running Press }} White can also force simplification with Lasker's 5.Qe2 Qe7 6.d3. This is generally only good enough for a draw, which Black should be satisfied with. Another possibility, explored by Keres, is 5.c4, known as the Kauffmann Attack.

A completely different approach is to meet 4...Nxe4 with 5.Nc3 Nxc3 6.dxc3 with rapid {{chessgloss|development}} and {{chessgloss|queenside}} castling. For instance, White can plan a quick Be3, Qd2, and 0-0-0, and play for a {{chessgloss|kingside}} attack, trusting that his doubled c-pawns will help protect his king, and that his initiative and attacking potential will offset the longterm disadvantage of having doubled pawns. In the 5.Nc3 line, Black must avoid 5...Bf5{{chesspunc|??}} 6.Qe2! which wins a piece due to the pin (if 6...Qe7 7.Nd5, forcing 7...Qd7 because of the threat to the c7-pawn; then 8.d3 wins the piece). Viswanathan Anand resigned after only six moves after falling for this against Alonso Zapata at Biel in 1988.{{cite web |url=http://www.chessgames.com/perl/chessgame?gid=1018015 |title=Alonso Zapata vs. Viswanathan Anand |website=ChessGames.com |access-date=13 June 2011 }}

The Cochrane Gambit, 4.Nxf7, is labelled "speculative but entertaining" by Nick de Firmian in Modern Chess Openings (MCO) 14th edition. He evaluates the position in Veselin Topalov–Vladimir Kramnik, Linares 1999 as offering chances for both sides after 4...Kxf7 5.Nc3 c5!? 6.Bc4+ Be6 7.Bxe6+ Kxe6 8.d4 Kf7 9.dxc5 Nc6.{{citation |last=de Firmian |first=Nick |author-link=Nick de Firmian |title=Modern Chess Openings |edition=14th |year=1999 |publisher=Random House |isbn=0-8129-3084-3}}

The Paulsen Variation, 4.Nc4, is labelled "ineffective" by de Firmian in MCO, but is occasionally seen at grandmaster level. US master Andrew Karklins has experimented with 4.Nd3!?, now called the Karklins–Martinovsky Variation. This was played in the World Chess Championship 2018 between Magnus Carlsen and Fabiano Caruana.{{cite web |url=https://www.chessgames.com/perl/chessgame?gid=1937789 |title=Magnus Carlsen vs. Fabiano Caruana, 2018 |website=Chessgames.com }}

3...Nxe4, the Damiano Variation, has traditionally been regarded as an error, though it has occasionally been seen in recent grandmaster play. Black must play accurately to avoid a serious disadvantage. After 4.Qe2 Black must avoid:

• 4...Nf6{{chesspunc|??}} 5.Nc6+ winning the queen
• 4...d5{{chesspunc|?}} 5.d3 Qe7 6.dxe4 Qxe5 7.exd5 and Black loses a pawn
• 4...d6? 5.Nxf7{{chesspunc|!}} Kxf7 6.Qxe4 and Black has lost a pawn and the ability to castle

Best is 4...Qe7 5.Qxe4 d6 6.d4 dxe5 7.dxe5 Nc6, and after 8.Nc3 Qxe5 9.Qxe5+ Nxe5 10.Nb5 (or 10.Bf4) White has the advantage.Janjgava, pp. 108–09Yusupov, pp. 12, 22–24

3...Qe7{{chesspunc|?!}} is inferior, as 4.d4 d6 5.Nf3 Qxe4+ 6.Be2 gives White a large lead in development.

3... Nc6?!, recently dubbed the Stafford Gambit, is considered dubious, but it sets a number of traps, and in the early 2020s it became popular in online blitz and bullet games. After 4.Nxc6 dxc6, White wins a pawn but must play carefully. After 5.e5 (5.d3 is better) Ne4 6.d3?? (White should play 6.Nc3, 6.d4, or 6.Qe2) 6...Bc5! and White resigned in Lowens–Stafford, US correspondence game 1950.{{cite web |url=https://www.chessgames.com/perl/chessgame?gid=1243149 |title=Lowens vs. Stafford, 1950 |website=Chessgames.com }}Forintos & Haag, p. 110 After 1.e4 e5 2.Nf3 Nf6 3.Nxe5 Nc6 4.Nxc6 dxc6 5.d3 Bc5, White must avoid the Légal Trap 6.Bg5?? Nxe4!, and if 7.Bxd8 (relatively best but still losing is 7.Be3) 7...Bxf2+ 8. Ke2 Bg4#. Instead White should play 6.Be2 Bc5 7.c3! with d3-d4 to follow, and Black has insufficient compensation for the pawn, though White must still play carefully.Avetik Grigoryan, [https://chessmood.com/blog/stafford-gambit-the-refutation Stafford Gambit ― The Refutation], Chessmood, 6 April, 2021

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| Steinitz Variation 3.d4

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| Position after 19.Nd2

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3.d4 was favoured by Wilhelm Steinitz, and is sometimes called the Steinitz Variation, although it was known earlier. Black can capture either pawn; also possible is 3...d6, transposing into the Philidor Defence.

After 3...exd4 4.e5 (4.Bc4 transposes into the Urusov Gambit) 4...Ne4 (4...Qe7?! 5.Be2 is better for White) 5.Qxd4 d5 6.exd6 Nxd6 7.Nc3 Nc6 8.Qf4 the game is approximately {{chessgloss|equal}}. After the other capture, 3...Nxe4, 4.Bd3 d5 (4...Nc6!? 5.Bxe4 d5, intending 6.Bd3 e4, is also possible) 5.Nxe5, when either 5...Nd7 or 5...Bd6 gives roughly equal chances.

A long and complicated tactical sequence which has frequently been seen in master games is 3...Nxe4 4.Bd3 d5 5.Nxe5 Bd6 6.0-0 0-0 7.c4 Bxe5 8.dxe5 Nc6 9.cxd5 Qxd5 10.Qc2 Nb4 11.Bxe4 Nxc2 12.Bxd5 Bf5 13.g4 Bxg4 14.Be4 Nxa1 15.Bf4 f5 16.Bd5+ Kh8 17.Rc1 c6 18.Bg2 Rfd8 19.Nd2 ({{em|diagram}}) and White has the slightly better endgame after either 19...Rxd2 20.Bxd2 Rd8 21.Bc3 Rd1+ 22.Rxd1 Bxd1 or 19...h6 20.h4.{{cite web |url=http://www.chessgames.com/perl/chess.pl?node=1150991 |title=Position Search after 19.Nd2 |website=Chessgames.com }}{{citation |last=de Firmian |first=Nick |author-link=Nick de Firmian |title=Batsford's Modern Chess Openings |year=2009 |publisher=Pavilion Books |page=136 |isbn=978-1906388294 }}

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3.Nc3 is the Three Knights Game of Petrov's Defence. It can also be reached via 2.Nc3 Nf6 3.Nf3 (the Vienna Game). 3...Nc6 transposes to the Four Knights Game. With the reply 3...Bb4 (or some others), it remains the Three Knights Game proper.

3.Bc4 is the Italian Variation of Petrov's Defence. With 3...Nc6, it transposes to the Two Knights Defence.

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| Position after 3.Bc4 Nxe4 4.Nc3

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Another possibility is 3.Bc4 Nxe4 4.Nc3, the Boden–Kieseritzky Gambit. It is not considered wholly sound, since Black has several viable options. Black can accept the gambit with 4...Nxc3 5.dxc3 f6, but must play carefully after 6.0-0 (for example 6...Bc5?? 7.Nxe5! is disastrous; 6...d6 and 6...Nc6 are good). Another more aggressive try is 6.Nh4, where White goes for a quick assault on Black's king, but Black can maintain a small advantage if he plays cautiously via 6...g6 7.f4 Qe7 8.f5 Qg7 9.Qg4 Kd8. Another possibility is returning the gambit pawn with 4...Nxc3 5.dxc3 c6 6.Nxe5 d5, which equalises. A third possibility is transposing to the Italian Four Knights Game with 4...Nc6, and if 5.Nxe4, 5...d5. If 5.Bxf7+?, then 5...Kxf7 6.Nxe4 d5 gives Black the {{chessgloss|bishop pair}} and control of the {{chessgloss|centre}}. If 5.0-0, Black plays 5...Nxc3 6.dxc3 and now Black can play 6...Qe7!, after which Bobby Fischer wrote that "White has no compensation for the Pawn",Bobby Fischer, My 60 Memorable Games, Faber and Faber, 1972, pp. 280–81. {{ISBN|0-571-09987-4}}. or 6...f6 transposing to the main line of the Boden–Kieseritzky. Black also has lines beginning 6...Be7 and 6...h6.

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• List of chess openings
• List of chess openings named after people

{{Reflist|30em}}

• {{cite book

|title=Petroff's Defence

|author=Forintos, Győző

|author2=Haag, Ervin

|publisher=Batsford

|year=1983

|isbn=0-7134-3202-0

|author-link=Győző Forintos

|author2-link=Ervin Haág}}

• {{cite book

|title=The Petroff

|author=Janjgava, Lasha

|publisher=Gambit Publications

|year=2001

|isbn=1-901983-46-3

|author-link=Lasha Janjgava}}

• {{cite book

|title=Beating The Petroff

|author=Kotronias, Vassilios

|author2=Tzermiadianos, Andreas

|publisher=Batsford

|year=2005

|isbn=978-0-7134-8919-4

|author-link=Vasilios Kotronias}}

• {{cite book

|title=Petroff Defence

|author1=Raetsky, Alexander

|author2=Chetverik, Maxim

|year=2005

|publisher=Everyman Chess

|isbn=1-85744-378-0}}

• {{cite book

|title=The Petroff: An Expert Repertoire for Black

|author=Sakaev, Konstantin

|publisher=Chess Stars

|year=2011

|isbn=978 954 8782 84-5

|author-link=Konstantin Sakaev}}

• {{cite book

|title=The Petroff Defence

|author=Yusupov, Artur

|publisher=Edition Olms

|year=1999

|isbn=3-283-00400-5

|author-link=Artur Yusupov (chess player)}}

{{Wikibooks|Chess Opening Theory|1. e4/1...e5/2. Nf3/2...Nf6|Petrov's Defence}}

• {{cite web |url=http://www.chessgames.com/perl/chessopening?eco=C42 |title=Petrov Defense (C42) |website=Chessgames.com |access-date=2007-04-26 }}
• [http://www.thechesswebsite.com/petrov-defense/ Petrov's Defence Video and explanation]
• [http://www.365chess.com/eco/C42_Petrov's_defence/games Petrov's defence (C42) – 365Chess.com ECO Games]
• [https://web.archive.org/web/20120306010747/http://www.chesscafe.com/text/lane74.pdf Gary Lane on the Cochrane Gambit]
• [https://www.bekemann.de/cochrane-gambit/boofreng.htm Cochrane Gambit theory]

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Category:Chess openings