The Three Knights Variation, Petrosian System is a variation of the Grünfeld Defense, catalogued as ECO D91. The line runs 1. d4 Nf6 2. c4 g6 3. Nc3 d5 4. Nf3 Bg7 5. Bg5, reaching the position shown below after 9 half-moves.
Both sides have pawns in the centre (White on d4, Black on d5), and one pawn capture is available, so the structure has not settled yet. Development is level at three minor pieces each. It is Black to move after five moves.
On the Grünfeld Defense generally: A hypermodern defense where Black allows White a big center then undermines it with ...d5.
You can play through this variation move by move in your browser — Learn mode walks the line with an explanation at each step, and Drill mode replays it from memory so you find out whether you actually know it. No account is required.
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The Three Knights Variation, Petrosian System goes 1. d4 Nf6 2. c4 g6 3. Nc3 d5 4. Nf3 Bg7 5. Bg5. It is a variation of the Grünfeld Defense and is catalogued as ECO D91.
The Three Knights Variation, Petrosian System is ECO D91. ECO codes group openings by their move order, so nearby codes cover closely related lines of the Grünfeld Defense.
Stockfish evaluates the position after 1. d4 Nf6 2. c4 g6 3. Nc3 d5 4. Nf3 Bg7 5. Bg5 at +0.08 at depth 18, which is balanced. Engine evaluation is only a starting point — at club level the practical value of a line is mostly about whether you know its plans better than your opponent does.
Both sides have pawns in the centre (White on d4, Black on d5), and one pawn capture is available, so the structure has not settled yet. Development is level at three minor pieces each. It is Black to move.