Material: Down a P. White has a substantial K-side attack based on local superiority in space and material. Only the Black Rg8 defends Kh7, which has one legal move, to h8. White has a battery Rg4 and Rg3 opposite Pg7 and Rg8. The White Ph5 controls the light square g6, while Qf4 and Nh4 can control dark squares around Kh7. The Black Rg8 must defend both Pg7 and Rc8, so Rc8 might become vulnerable to a Q-fork. The White Nh4 is not particularly active yet.

Candidates (29.): Rxg7+, Qxh6+, Nf5

29.Nf5 (threatening 30.Rxg7+ 31.Rxg7+ 32.Qxh6 #)

Black can accept the sacrifice of Nf5.

29…exf5 30.Rxg7+ Rxg7 [Kh8 31.Qxh6#] 31.Qxf5+ Kh8 [or Kg8]

[31…Rg6 32.hxg6+ then 33.Qxc8 and Black drops material]

32.Qxc8+ Kh7 33.Qf5+ Kh8 [or Kg8] 34.Rxg7 Kxg7

[else, drop material or mate]

35.Qf6+ Kf8 [else, 36.h6 and mate soon]

36.h6 (threatening 37.h7 38.h8=Q#]

Black cannot stop Ph6 from h8=Q.

Black must therefore refuse the sacrifice and try to protect g7 against the mate threat.

29…f6 30.Rxg7+ Rxg7 [else, drop Qa7 or be mated]

31.Qxh6+ Kg8 32.Rxg7+

a3!

A powerful move. Chases the knight off its powerful b4 outpost, and prevents another loss of a valuable pawn since material is the most mathematical way to evaluate chess, and math doesn't lie.

This also prepares our pawn for an eventual promotion after we clear up the queenside, since it is now one step closer.

29…exf5 30.Rxg7+ Rxg7 [Kh8 31.Qxh6#] 31.Qxf5+ Kg8 32.Qxc8+ Kh7 33.Qf5+ Kg8 34.<Rc3>

but I forgot the Ph6 blocks the immediate threat h8=Q, so my 34.Rxg7 fails.

if e6x[N]f5 31. Qxf5+ assuring the capture of what is now a loose rook – oops and mating (... a sweet point is if Black plays Kh8 White can even be artistic and play Qf6)

This is an exceptional training position – the useful vs. the useless knight

If this starts with a queen sac I may have to box my pieces once and for all :)

I timed out – spending way to much effort on g6 –visualizing a combo with the Queen mating on h3. I finally tried by moving the pieces to see if there was more than by eye could see - and I admit I was a little fuzzy and uncertain as I found 30....Rg5 instead of the knight capture. But 31. Nxh6! and all is well: time to look.....

I have a shorter look to Qf6, Rg6, Rxg7 and Ng6, but none of them worked out.

I think the solution starts with 29. ♘f5!. Threat: ♖xg7 with mate. So 29...exf5 is the only move for Black. 30. ♕xf5+ Black has 2 options, both not enough to survive: A. 30...♔h8 31. ♖xg7 ♖xg7 (or mate in one) 32. ♕f6! and Black is lost (either on g7 or h6, depending on blacks answer). I haven't checked the option 32. Qxc8 as Qf6 is much more forcing. B 30...g6 31. fxg6 ♖xg6 32. ♖xg6 33. ♕xg6+ ♔h8 34. ♕xh6 ♕h7 35. ♕f6+ and mate in a few moves.

Yes... but we've come all this way might as well go to mate -- 35...Qa6 37.hxg7+ Kh7 38.Rh3#

Omg. I solved this puzzle! And to think it only took me a little more than an hour moving the pieces set up on a board -- we're not playing touch move, are we? ;)

click for larger view

White’s best line might now be 29 a3 Nc6 30 Nf5 Rc1+ 31 Qxc1 exf5 and white is up just a rook for a knight and pawn.

click for larger view

Looking at the position, it was clear that I had superior K-side firepower, but black's pawns completely restricted my Q and N from making offensive progress and his R+K otherwise provided adequate protection of g7.

Such conditions scream for a sacrifice to bust his pawn defense and then find the winning continuation. Usually, the best sac is one that allows our Q to join the attack *with check*.

I started out with 29.Rxg7+, etc., which looked promising since my Q comes to f6 with check, leaving me trying to win with Q+N. However, the black king always escapes by running to the Q-side.

So, I backed up and noticed another promising idea: Sac the knight on f5!

29.Nf5 <puts another attack on g7, forcing...> exf5 <and again, allowing my Q to attack with check>

30.Qxf5+ <This is better: My Q has access to both f5 and f6, I still have both rooks, my e pawn is mobile, and black's K has no path to the Q-side. Black only has...> Kh8 <30...g6 31.hxg6 leads to R exchanges with Q+R vs naked K. But now the K is vulnerable from both f6 and h6>

The rest flows pretty naturally (which is fortunate since I'm on the edge of my board vision already).

31.Rxg7 <threat:Qh7#> Rxg7

32.Qf6 <pinning the rook and threatening Ph6, let alone Qxg7#> Rg8 <only way to prevent mate>

33.Qxh6+ <another defender gone, and now my h-pawn is mobile> Rh6 <forced>

34.Qf6+ <black has no time to breathe> Rhg7 <now the rook is pinned again; if 34...Rgg7 then 35.Qd8+ w/ mate next>

28 ... Qe7

is the only way for black to avoid catastrophe. It plays out

28 ... Qe7
29 a3 Nc6
30 Nf5 Rc1+
31 Qxc1 exf5
32 Rf4 Qd7

click for larger view

After Nf5 it is a forced mate if Black takes the Knight, so arguing over alternative moves or move orders is pretty silly. Also, Qxf5 is the only good move here...again it forces mate whereas playing Rxg7 here only leads to a draw at best.

But even funnier is that Nf5 forces mate REAGARDLESS of black reply!! If you leave the Knight there then Rxg7+ becomes crushing against most other replies. The point being that after Rxg7 Qxh6 is crushing. And trying to block the file by g6 or g5 fails to hxg6+ with mate still coming.

According to Toga II 1.3.1,

<<johnlspouge> wrote: Toga gives value +1.38 to

29…exf5 30.Rxg7+ Rxg7 [Kh8 31.Qxh6#] 31.Qxf5+ Kg8 32.Qxc8+ Kh7 33.Qf5+ Kg8 34.<Rc3>>

...30.Rxg7+ Rxg7 31.Qxh6+ or,
...30.Rxg7+ Qxg7 31.Rxg7+ Rxg7 32. Qxh6 with 33.Qxg7# to follow.