user30437: I just failed a puzzle at chess.com, despite being 2 moves away from check mate. I am quite sure that there is no move I could have made to get check mate in 1 move, so I am wondering how I failed.
I just looked at the suggested solution, which would be moving to g3 instead, why is that better than my move?


user9363: For future puzzles provided by chess.com specifically, the puzzle controls also offer engine analysis, which can be very helpful for figuring out why you move is incorrect. You can see the computer refute your move by trying it out in the analysis. I've highlighted the button in a yellow box:


user26335: As pointed out by Michael West, 1...Nf2 provides White the opportunity to exploit White's overwhelming advantage whereas 1...Ng3 is a forced checkmate in three (i.e., Black has a guaranteed win).
Black is down too much material and has no compensation if they cannot force mate. After 1...Nf2??, Black is utterly lost.
Stockfish 14+ NNUE confirms this (+9.8, depth = 27, 8115k nodes/s). Despite the low depth, the example lines provided illustrate the point.
[FEN "8/2Q2pk1/3p2p1/NP1Np3/4n2p/7P/6PK/r7 b - - 0 1"]

1...Ng3! 2. Qxf7+ Kxf7 3. b6 Rh1# {Black wins} (1...Nf2?? 2. g4 hxg3+ 3. Kxg3 Ne4+ 4. Kf3 Ng5+ 5. Ke2 Ne6 6. Qxd6 Kh7 7. Nc4 e4 8. Qe5 Ra4 9. Nf6+ Kh6(2. g3 Ne4 3. gxh4 Ra2+ 4. Kg1 Ra1+ 5. Kg2 Ra2+ 6. Kf3 Nd2+ 7. Ke3 Nf1+ 8. Ke4 Ng3+ 9. Kd3 e4+)) 

Note: Diagram from Black's point of view to match OP's diagram.

user17425: g3 is a better square for the Knight because it blocks White's g-pawn and so prevents White playing g3 or g4.

30437: <p>I just failed a puzzle at chess.com, despite being 2 moves away from check mate. I am quite sure that there is no move I could have made to get check mate in 1 move, so I am wondering how I failed.</p>
<p>I just looked at the suggested solution, which would be moving to g3 instead, why is that better than my move?</p>
<p><a href="https://i.stack.imgur.com/xC0Uu.png" rel="noreferrer"><img src="https://i.stack.imgur.com/xC0Uu.png" alt="Move classified as incorrect" /></a></p>
 9363: <p>For future puzzles provided by chess.com specifically, the puzzle controls also offer engine analysis, which can be very helpful for figuring out why you move is incorrect. You can see the computer refute your move by trying it out in the analysis. I've highlighted the button in a yellow box:</p>
<p><a href="https://i.stack.imgur.com/Ifwdv.png" rel="noreferrer"><img src="https://i.stack.imgur.com/Ifwdv.png" alt="Engine analysis tool" /></a></p>
 26335: <p>As <a href="https://chess.stackexchange.com/a/37520/26335">pointed out</a> by <a href="https://chess.stackexchange.com/users/17425/michael-west">Michael West</a>, <strong>1...Nf2</strong> provides White the opportunity to exploit White's overwhelming advantage whereas <strong>1...Ng3</strong> is a forced checkmate in three (i.e., Black has a guaranteed win).</p>
<p>Black is down too much material and has no compensation if they cannot force mate. After <strong>1...Nf2??</strong>, Black is utterly lost.</p>
<p>Stockfish 14+ NNUE confirms this (+9.8, depth = 27, 8115k nodes/s). Despite the low depth, the example lines provided illustrate the point.</p>
<pre><code>[FEN &quot;8/2Q2pk1/3p2p1/NP1Np3/4n2p/7P/6PK/r7 b - - 0 1&quot;]

1...Ng3! 2. Qxf7+ Kxf7 3. b6 Rh1# {Black wins} (1...Nf2?? 2. g4 hxg3+ 3. Kxg3 Ne4+ 4. Kf3 Ng5+ 5. Ke2 Ne6 6. Qxd6 Kh7 7. Nc4 e4 8. Qe5 Ra4 9. Nf6+ Kh6(2. g3 Ne4 3. gxh4 Ra2+ 4. Kg1 Ra1+ 5. Kg2 Ra2+ 6. Kf3 Nd2+ 7. Ke3 Nf1+ 8. Ke4 Ng3+ 9. Kd3 e4+)) 
</code></pre>
<p><sub>Note: Diagram from Black's point of view to match OP's diagram.</sub></p>
 17425: <p>g3 is a better square for the Knight because it blocks White's g-pawn and so prevents White playing g3 or g4.</p>
