Caissa Codex
C42

Petrov's Defense: Classical Attack, Mason-Showalter Variation

Chess diagram: Petrov's Defense: Classical Attack, Mason-Showalter Variation after 6…Nc6

Type a move and press Enter: e4, Nf3, O-O, or from and to squares like g1f3 (e7e8q to promote). The board is also played with the mouse.

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Statistics from Lichess

140,398 games: White 46.2% / Draw 8.0% / Black 45.8%

The moves played next. Pick one to see it on the board.
Next moveGamesWhite / Draw / BlackW / D / B
106,208106K
11,92012K
8,5258,525
5,5125,512
2,4782,478
2,0552,055
1,6001,600
614614

Rated Lichess games between players rated 1600 to 2500, from the Lichess opening explorer, updated Nov 1, 2026

Engine evaluation

+0.34 White is slightly better

Best play: 7. O-O Be7 8. Nbd2 Nxd2 9. Bxd2 O-O 10. c3 Bg4 11. h3 Bh5

Stockfish 19, depth 30, after the line's last move. Scores are in pawns, from White's side.

Overview

Petrov's Defense: Classical Attack, Mason-Showalter Variation (ECO C42, Open Games) is a variation of Petrov's Defense: Classical Attack, reached after 1. e4 e5 2. Nf3 Nf6 3. Nxe5 d6 4. Nf3 Nxe4 5. d4 d5 6. Bd3 Nc6 (6 moves).

In 140,398 rated Lichess games between players rated 1600 to 2500, White won 46.2%, Black 45.8% and 8.0% were drawn. White's most played move here is 7. O-O, in 76% of those games.

It branches into 2 named variations; the most played are Petrov's Defense: Classical Attack, Jaenisch Variation and Petrov's Defense: Classical Attack, Krause Variation. In all, 4 named lines continue from it.

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How to play against Petrov's Defense: Classical Attack, Mason-Showalter Variation

The most played answer, 7. O-O, also scores best for White: 51.3%, with White winning 47.3% and Black 44.6% of 106K games. Of the main answers, 7. c4 scores lowest: 44.9%. Stockfish's first choice is also 7. O-O.

Main answers: those played in at least 5% of these games. Score: White's wins plus half the draws, in rated Lichess games between players rated 1600 to 2500. How to play against other popular openings

Variations (2)

Other lines from the same position

Instead of 5…d5 6. Bd3 Nc6, the position after Petrov's Defense: Classical Attack also goes on to:

All 4 named lines that continue from here

Cite this page

Caissa Codex. “Petrov's Defense: Classical Attack, Mason-Showalter Variation (C42)”. Lichess data as of 1 Nov 2026. https://chesscodex.org/openings/petrovs-defense-classical-attack-mason-showalter-variation

https://chesscodex.org/openings/petrovs-defense-classical-attack-mason-showalter-variation