(a) 37...bxc6 38 Qxf7 Kxf7 39 b7, and promotion.
(b) 37...Qxc7 38 bxc7 Bf5 39 Ne7+, and promotion.

So, what other options does black have? White is threatening a royal knight fork on e5, so black needs to move the queen or king.

(c) 37...Qe4+ 38 Qxe4 fxe4 39 Ne5+, winning the bishop.

The best I can find is

(d) 37...Kg7 38 Nd8 Qxc7+ Bf5, and white will win black's bishop.

Time to check.

F.1) 40.Ng6+ is *not* mate, but 41.Qg3 is!

37 Nc6 appears to win a Pawn:
A 37...Qf4+ (best) 38 Qxf4 gxf4 39 Ne7+ Kf6 40 Nxd5 Ke5 41 Nb4 Ke4!? 42 g4 fxg3+ 43 Kxg3 Bf5 44 h4 and White a Pawn up should be winning but there is plenty of play in the position; B 37...bxc6? 38 Qxf7+ 1-0
C 37...Qxc7? 38 bxc7 Bf4 39 Ne7+ 1-0
D 37...Bd4? 38 Ne5+ 1-0 but NOT 38.Qxf7+? Kxf7 39 Ne8+ Kf6 40 Nxb7? d4! 0-1
E 37...Qf6?! (hoping for Qxb7? Qf4+) 38 Ne5+ wins the Bishop F 37...Kg7 (to avoid the fork on e5) 38 Qxf7+ and 39 Ne5+ wins the B. Time to see how things went:
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37..Qf1 was played protecting the B. After 39...Qxd3 White can safely play 40 Qxb7 etc. with an easy ending since there is no longer a perpetual check. No doubt this is why Black resigned. Time to look at the kibitzes. ====
Not a good day! In my line A, I fail to spot that 39 Ne5+ wins the Bishop. Thanks <VincentL> and <agb2002>. <After 39...Qxd3 White can safely play 40 Qxb7 etc> - <VincentL> has posted the skewer Qh7+ (much better). As <gofer> points out, after 37...Qf1 38 Ne5+ Kh5 (instead of Kf5) walks into a mating net.

Crafty End Game Trainer check of the puzzle position:

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Material: White has a N for B.

Ideas: I think white's best shot right here is to play Ne5+ and hope is opponent doesn't notice it's illegal.

...While that's a bit wishful, the idea is still good: White would like to play Ne5+ . How can his N maneuver there? He has Nd4-f3 or Nd4-c6 as possible routes. Nc6 is more threatening because his N is moved further up the board and is immune to capture due to the b6 pawn. 37. Nc6 should be it.

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A) 37...Qxc7 38.bxc7 Bf5 39.Ne7+ followed by 40.Nxf5 and 41.c8=Q

B) 37...bxc6 38.Qxf7+ Kxf7 39.b7

C) 37...Qf4+ 38.Qxf4 gxf4 39.Ne5+ and 40.Nxd3

D) 37...Bf5 38.Ne5+ winning the queen and the game.

I saw nothing else forcing and no threats from black so that's where I stopped. But is there anything else forcing? Looking back over my analysis, Qf7 is perhaps another forcing move to consider even though it is easily defeated with 38.Ne5+ and 38.Nxd3.

That pretty much does it for forcing moves. But <David2009> helped me realize yesterday that just because all forcing moves by black (in this case) is winning for white it doesn't mean Nc6 is best. That's because black has at least one non-forcing move to stop the knight forks winning the bishop or queen. If any non-forcing replies defeat white's plan of winning material then it is possible there could be a better move besides Nc6. There could be anyway, but it shows that if you have the time to do so, you should try developing a more complete list of candidates before falling in love with a single candidate that looks like it wins or draws from an otherwise losing position. If the non-forcing game move 37...Qf1 prevented black from losing material it may be that Nc6 should be reconsidered and perhaps Nf3 should be examined more closely.

Let's play the ending out against Crafty EGT starting 38.Ne5+ Kf6:

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D Howell vs N Giffard, 2009 White 38? http://www.chessvideos.tv/endgame-t... Exchanging the Bishop is the natural way to go IMO since we know from endgame theory that Q+Pb7 vs Q is a win if (a) the enemy king is cu off and (b) the White King can shelter from the checks. So we continue 39.Nxd3 Qxd3 40.Qxb7 Qxc3 to reach

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There is now a cunning quick win starting 41. Qc7! d4 42 Qd8+ Kf5 43.b7 which I leave you to explore. However OTB and my instinctive choice is the slower but thematic win starting 41.Qxd5 Ke7 42.b7 Qc7+.

click for larger view

Howell-Gifford Queen ending variation 42? http://www.chessvideos.tv/endgame-t... White now has to escape the checks. This is tricky but can be done in several ways. The most thematic way is with Kg1. Firms time around I messed it up. Second time around I remembered the cross-check strategy one would use in the bare KQP vs KQ ending (i.e. ignoring the King side pawns): 43.Kg1 Qc1+ 44.Kh2 Qf4+ 45.Kg1 Qc1+ 46.Kf2 Qf4+ 47.Ke2 Qc7 48.Kd3 Kf6 49.Qb5 Qg3+ 50.Kc4 Qf4+ 51.Kb3 Qg3+ 52.Ka2 and promotes safely.

There are interesting wins starting 43. g3 Qc2+ which I leave you to explore.

Playing it out with Fritz, my choice of 37. Nf3 to also seems to work, but the winning technique is longer and more difficult.

Instead, 37. Nc3! is much easier, because in the variation 37...Qxc7+ 38. bxc7 Bf5, White has the Knight fork 39. Ne7+ available to remove the pesky Bishop and quickly clear the way for the pawn on b3 to promote.

In the 37. Nf3 line, after 37...Qxc7+ 38. bxc7 Bf5 39. Nd4 Bd7 40. Nb5! White will be able to win the Bishop and has good winning chances in the ensuing Knight versus pawns endgame. But the win is tricky and much more difficult.

So, it is much better to play 37. Nc6! where the access to the e7 square for the Knight fork enables White to promote the pawn with an easy win.

Fair point, I suppose I don't think my comments have any longevity, so I don't think about them ever being read in the future. I will try to improve...

In passing, Crafty EGT does come unstuck quite quickly...

depth: 19 : 6 min :
White error
(=0.11):9.Ne5. Best, 0.00, 0.52.

depth: 22 : 5 min :
Black blunder
(+2.00):35...Qf7. Best, Kf6, 0.59.

depth: 22 : 6 min :
Black blunder
(+8.95):36...Kg6. Best, Kg8, +2.20.
h5, +2.30.

White to play (37.?) "Medium"

My first thought was to play 37. Nf3, seeing the fork on e5, but after 37...Qxc7 38. bxc7 Bf5 39. Nd4 Bd7!, White's knight can't help promote the pawn. From here (after 38...Bf5), I saw that a knight check on e7 would win, leading me to look to see if 37. Nc6 was playable instead of 37. Nf3. Turns out, it is!

37. Nc6!!

Now 37...Qxc7 is not playable as shown above (38. bxc7 Bf5 39. Nd7+), and neither is 37...bxc6 38. Qxf7+ Kxf7 39. b7 and the pawn will promote. Black must find a defense to both 38. Ne5+ and 38. Qxf7+ Kxf7 39. Ne5+. So we can eliminate king moves as well as bishop moves. If 37...Qf5 38. Ne7+ wins the queen. This leaves one reasonable try.

37...Qf1 38. Ne5+

And not 38. Qxb7? Qf4+ 39. Kg1 Qf1+ with a perpetual check.

38...Kf6

A quicker finish is 38...Kh5 39. g4+ Kh4 40. Qg3# or 38...Kf5 39. Nxd3 Qxd3 40. Qh7+ with a killing skewer.

39. Nxd3 Qxd3 40. Qxb7 Qxc3 41. Qc7

I looked at three candidates: 37 Qxf7+, 37 Nf3 and 37 Nc6

couldn't figure out the subvariation of 37 Nc6

always analyize the most forcing move:

a)37 Qxf7+ Kxf7 -

a1) 38 Nc6 Ke8 39 Na5 Ba6

a2) 38 Nb3 Bb5! 39 Nc5 (if 39 Na5 Ba6 ) Bc6 : this didn't work out

b) 37 Nf3

b1) 37...Qxc7? 38 bxc7 Bf5 39 Nd4 Bd7 40 Nb5! Kf6 41 Nd6 Ke5 42 Nxb7! d4 43 cxd4+ Kxd4 44 Nd6

b2) 37...Qf5 38 Ne5+ Kf6- I don't see any way for white to make progress

c) 37 Nc6 Qf1 38 Ne5+ and now:

c1) 38...Kh5? 39 g4+ Kh4 40 Ng6+! Bxg6 41 Qg3#

c2) 38...Kf5 39 Nxd3- Black drop a piece due to the skewer along the b1-h7 diagonal

c3) this is the variation I was stuck on

38...Kf6 I opt for 39 Qd6+ Kg7 40 Qe7+ Kg8-

I could not find a way to breakthrough from here and Black is threatening the perpetual Qf4+: I missed the winning queen ending after 39 Nxd3