White mates as follows:

37.Nf6+!

Black is oblidged to capture, because 37...Kh8 allows 38.Qh2+ and mating.

37...Bxf6 38.gxf6

Now the threat is 30.Qxf8+ and mates.

The black queen can give a meaningless check with 38...Qa1+ leading to nothing after 40.Kg2.

It appears that black has to move the rook. If the rook goes to c8, b8 or a8, then Rd8+ leads to a quick mate.

So let's try 38...Re8:

Still white plays 39.Rd8.

The first idea is 37.Nf6+ Bxf6 (37... Kh8 38.Qh2+ Bh6 39.Qxh6#) 38.gxf6 (threatening 39.Qxf8+ Kxf8 40.Rd8#):

A) 38... Re8 39.Qe7 Rxe7 (39... Rf8 40.Qxf8+) 40.fxe7 Qa1+ 41.Kg2 Qe5 42.Rd8+ Kg7 43.e8=Q Qg5+ 44.Kf1 + -.

B) 38... R(a-c)8 39.Rxf7 + - (39... Kxf7 40.Qe7+ Kg8 41.Qg7#).

C) 38... Qa1+ 39.Kg2 Re8 40.Qe7 Qe5 41.Qxf7+ Kh8 42.Qh7#.

Hmm. A knight check is a natural place to start. 37 Nf6+ Bxf6 (not Kh8, 38 Qh2+) 38 Qxf6 planning Rd4 and Rh4, what defence does black have to that? His only option must be a series of queen checks as he can’t move his Rf8.

So lets try 38 …. Qc2; 39 Rd4, Qc1+; 40 Kg2 and there are no more checks even though white will need to play Rh4.

Or 38 ….Qxb4; 39 Rd4, Qe1+ (or Qb1+); 40 Kg2 and again no more checks

That looks OK (if I was white against Bacrot I’d be happy with it! ☺).

Alternative is 37 Rd8 (threatening Nf6+). 37 … Qa1+ 38 Kg2 doesn’t help black. Nor does 37 … Rxd8; 38 Qxd8+ Bf8; 39 Nh6+, Kg7; 40 Qf6+.

However 37 Rd8, Rxd8; 38 Qxd8+ Kh7; 39 Nf6+, Bxf6; 40 gxf6 Qxb4 might hold 41 Qe7 Qb1+; 42Kh2 Qa2 not pretty (and there may well be a win at the end of that but not that I can calculate at this time of day!).

Time to see what I have missed …..

OK, well I missed the solution! - looks like everyone else voted for gxf6 seeing the Qxf8 idea that I had missed.

37.Nf6+ Bxf6 (Kh8 38.Qh2+ forces mate) 38.gxf6 threatening 39.Qxf8+! and mate next.

Now the hampered mobility of the black queen limits black's options:

A) 38... Re8 39.Qe7! Rxe7 (Rf8 40.Qxf8+ Kxf8 41.Rd8#) 40.fxe7 Qa1+ 41.Kg2 Qe5 42.Rd8+ Kg7/h7 43.e8/Q wins.

B) 38... Rc8/a8 39.Rxf7! Kxf7 40.Qe7+ Kg8 41.Qg7#

B.1) 41... Rc1+/Qa1+ 42.Kg2 and black has no good defense against 43.Rg7+ Kh8 44.Qh2#

C) 38... Qa2(a3/b3/c2) 39.Qxf8+ Kxf8 40.Rd8#

D) 38... Qa1+ 39.Kg2 Re8 39.Qe7 transposes to A

D.1) 39...Rc8/a8 40.Rxf7 transposes to B.

As for the timing on this solution, Nf6+ is an obvious continuation and was a quick find. Trickier for me was improving on 38...Rc8 39.Rd8+? Rxd8 40.Qxd8+ Kh7 41.Qe7 (Qf8? Qa1+) Qa2 and black holds. In general, avoid simplification / reduction of tension unless you are sure of your advantage!

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It seems that <36...Bg7?> is the blunder that cost the game - not obvious to me though. Black is trying to prevent Nh6+. There's quite a difference between the suggested move of <36...Kg7>

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[+0.88] d=18 36...Kg7 37.Nh6 Qxb4 38.Qxb4 Bxb4 39.Rxa7 Bd6 40.Rd7 Be5 41.Kf1 Bc3 42.Rb7 Bb4 43.Kg2 Bd6 44.Kf1 (0:02.35) 21586kN

Both Nh6+ and Qxf8+ seem either useless or losing.

37.Nf6+ Bxf6 (37...Kh8 38.Qh2+ Bh6 39.Qxh6#) 38.gxf6

This threatens 39.Qxf8+ Kxf8 40.Rd8#. Black has useless checks on a1 and d1, but I don't see a decent defense for black.

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34.Qd6,
This is good, but it is not the only move for White in this position.

[The box likes: (>/=) 34.Kg2, here for White, and so do I. (34.Kg2, a slight plus for White - Fritz 11.) ]

34...g6!?; (Is this necessary?)
I am not even sure about this move, it does weaken the dark squares a lot. (However, Bacrot was in zeitnot here, and maybe was worried about Leko eventually playing g5-g6. My first impulse was to play 34...Qb3; in this position.)

However, after checking things with the box, it seems that "the iron monster" agrees with Bacrot, 34...g6 might be forced (or best).

35.Nh2!?, (hmmm)
This gives White a win, but probably was not the best move for White.

[Better was: >/= 35.Qc5, with a slight plus for White, - Fritz 11.]

35...Bc3;
The best move here for Black.

36.Ng4 Bg7?; (Really - '??')
Black throws away a pretty decent position with this one errant move.

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Now we have reached the position for ChessGames P.O.T.D. ("Problem of the Day.")

[After the following moves: >/= 36...Qxb4; 37.Qxb4 Bxb4; 38.Rxa7, (with an advantage) I think that it would be problematic (at best!) for White to win - from here. ]

White to play and make his 37th move in this position.

37.Nf6+,
Sometimes the most direct move is the best move.

[Less effective would be: </= 37.Kg2?! a5; 38.Rd8±.]

37...Bxf6[]; (Box.)
This is completely forced.

[Of course not: </= 37...Kh8??; and now 38.Qh2+, ( ) and it's mate next move. ]

38.gxf6, (The most aggressive.)
This is the best move for White.

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Now White has many threats. You have to be a pretty decent player to see that White threatens a simple win here: 39.QxR/f8+!, KxQ/f8; 40.Rd8#.

In this position Black should play ...Re8. Another (less obvious) win would be: 38...Re8[]; 39.Qe7!, RxQ/e7; Black may as well take, to retreat to f8 allows QxR+, winning.) 40.fxe7, and Black cannot prevent White's pawn on e7 from promoting.

[</= 38.Qxf6? Qxb4; 39.Rxa7, "="]

Now Black is quite lost, however Fritz shows that playing the Rook to e8 was the only decent try for Black.

38...Rc8!?; (Maybe '?!' or '?') 39.Rxf7!,
Black resigns. (Taking the Rook allows Qe7+ and mate next move.)

1-0

to reiterate the remainder of Dzechiel's solution...

39.e7! (39.e7?! f8) 39...xe7 40.fxe7
a1+ 41.g2 e5 42.d8+ g7 43.e8=

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What follows is 37…Bxh6 38 gxh6 Qa1+ 39 Kg2 (all look forced), then 39... Re8 (to prevent h7+)

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Now 40 Qf4 (threatening Qxf7) Rf8 (forced) 41 Rxa7! (If 41…Qxa7, 42 Qf6, winning the queen) Qd1 42 Ra5 Qd5+ 43 e4 Qd4 44 Rxb5.

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What I found was that if black doesn't play Bg7 then white can even not play Nf6 and instead dance around the black king (if black takes the Knight when it moves to f5 then it gets caught with Qh6+ Kg8 g6 mating!), so we might get...

36 ... Qa1+
37 Kg2 Qb2?/a6?

38 Nh6+ Kg7 (protecting the rook)
39 Nf5+ Kg8 (protecting the rook)
40 Ne7+ Kg7 (not allowing Qh2+ mating)
41 Nxg6 Re8 (there could be better but lets assume not...)

42 Ne7 Kf8 (to avoid Qh6#)
43 Nf5+ Kg8 (forced)
44 Nh6+ Kh8 (to avoid Rxf7+)
45 Nxf7+ Kg8 (to avoid Ne5+ mating)
46 Nh6+ Kh8 (forced)

So the knight has cleared all blacks defenses...

:-)