Find the winning move for black

I analyzed this game using Crafty and my last move Rae1 was a blunder. Can you find the winning move for Black?

....and whatever white does to prevent mate results in the loss of the Q after black plays 19......Nh3+

Right. Hard to see in a game though.

I find that doing engine analysis of games only makes me a worse player because I become paranoid about making mistakes and hence do not play fluently. I just beat a 1770 on FICS and then did an engine analysis and found that I had made a blunder which the 1770 did not see. If that had been a tactics trainer problem most people would have been able to see it but neither me nor my opponent saw it. But it was a game and it's hard to treat every position as if it were a tactics position because only 5% of positions are like that.

no, even beginners can find that move.

i was taught early that the moves to consider first are checks, captures, checks.

both of blacks checks are obviously bad, both captures don't really lead to anything.

then you consider the only threatening move on the board and see it wins instantly.

its the quiet moves that are hard to find, people are not taught to find those moves.

needless to say it took me 5 seconds to find qg5

I use an engine to analyze my games and NEVER compare my moves to the engine moves. What would be the point? It would be like comparing my moves to an IM's moves.

Instead, I look at it as a teacher for some aspects of my game. I feel this approach has actually made me braver, for lack of a better term. It often shows me possibilities I would have never thought have. No doubt I've learned a lot from chess engines.

Most novice players could solve that puzzle for sure.

But I think very few would find it during a game. They'd have to be lucky enough to be looking for a tactic. As pdve says most people don't have the discipline to look for tactics on every move (even if they were taught this, and are told 1000 times).

I agree that most people don't look for tactics every move. But I really doubt even top players do this. It would be so tiring .

Instead I believe, from things I've read, they look for situations that can lead to possible tactics. For example, looking for 2 or more weaknesses that can be exploited. 

I found the solution to the puzzle above quickly as well, but not because I was looking for a tactic, but rather because there were two exploitable weaknesses. The tactic revealed itself.

whites king looks fairly undefended with no pieces guarding g2, h2.

at this point you should consider attacking moves like nxg2,nh3+.

then you look at qg5 and see that it wins instantly.

honestly when you see an undefended white king, attacking moves should be considered first, the position looks ripe for tactics.

I may be wrong here. White has an interesting response of 19 Bxh7+

Have not the time to analyse it, but I think white gets to keep his Q and escape immediate checkmate albeit for the cost of his bishop. Black looks better overall though.

lagomorph,

Crafty gives Bxh7+ as the only alternative but still with an evaluation of -3.1 meaning that Black is winning.

Agreed this move is obvious. It is a direct mate threat for white has limited options. This would be the first move I would consider if I were black.

Right, they don't make a list of every threat and capture like a beginner is almost forced to if they hope to find tactics.

I don't even think they consciously look for signs of a tactic on every move.

In fact I think most of chess is played at a near subliminal level.

if so then.....

19 Bxh7 Kh8

20 Ng6+ Kxh7   (black cannot play Nxg6 or his own Qis at risk)

21 Nxf4         

so same scenario....white escapes immediate checkmate for cost of his Bishop.

I agree. White is just lost after Qg5.

you type too quickly for me !