White's loose bishop prevents him from winning material with Rde1, but the e-file is still the Achilles Heel of Black's position.

21.d6! Nxd6.

(21...Qd8 22.Bxe5; 21...Qxd6 22.Qe2, 21...Nxc4 22.dxe7)

22.Ba2!!

The only square; 22.Bd5 runs into a pin on the d-file, 22.Be2 blocks the e-file, and 22.Bb3 c4! opens up c5 for the Queen.

22...Ndc4

(otherwise Rde1)

23.Qe2! Bxc3
24.bxc3 Qe6
25.Bg3

<21 d6 ...>

21 ... Nxc4
22 dxe7 Nxd2
23 exf8=Q+ Kxf8
24 Rxd2

21 ... Qd1/Qd2
22 Bxe5

21 ... Qxd6
22 Bxe5 Qxe5
23 Rfe1 Qf5
24 Qd5 Bxc3 (Qxd5 Nxd5! )
25 Qxf5 gxf5
26 bxc3 g6
27 Re7/Rd7

Now we come to the star of the piece!

21 ... Nxd6
22 Nd5!!!

At this point, I have given up. I really want to play 22 Nd5, but I dont think it works...

~~~

What gives White a pull is the lurking pin vs Knight on <e5>, combined with the fact Black can't very well shore up the Knight with 21...f6 since this opens the a2-g8 diagonal, and finally, the passed d-pawn. These three aspects coordinate wonderfully to give White a winning position.

I first looked at 21.Qe2 (which I think is winning positionally) but settled on 21.d6 which is immediately forcing and more in Yusupov's style

<21.d6> 21...Nxd6 (21...Nxc4?? 22.dxe7 Nxd2 23.exf8=Q+ Kxf8 24.Rxd2 and White is up a rook) 22.Ba2 c4 (necessary to block the diagonal; bad for Black is 22...Nf5? 23.Rde1 Rfe8 24.Bxe5 and White has won a piece) 23.Nd5 Bc5+ 24.Kh1 Qe6 25.Nc7 Qe7 26.Nxa8 Rxa8 27.Qd5 forking the Bishop and Knight::

click for larger view

I don't see a reasonable move or continuation that allows Black to either recover the material or somehow gain a positional edge

*****
Of course, 25.Bxe5 is more to the point since 25...Qxe5 26.Re1 Qf5 27.Ne7+ forks the Black Queen

<al wazir: I went with 21. Qe2 too. Didn't see 21...Nd6.>

Also went for 21. Qe2 thinking it's an easy pin 'em and win 'em combination, but missed the neat defense 21. Qe2 Nd6!

So in addition to another deep, attacking Saturday puzzle combination, we also get a lesson on using a counter attack to defend against a pin.

21 Qe2 Nd6
22 Ba2 Bxc3
23 bxc3 f6
24 gf gf
25 Bh6

Morf, black can play 23...Rad8 in this line.

click for larger view

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Black threatens 21... Nxc4.

White can pin the knight on e5 with 21.Re1 but Black simply plays 21... Nxc4. In the case of 21.Qe2 or 21.Qe3 the answer 21... Nd6 seems to solve Black's problems (22.Bxe5 Nxc4; 22.Qxe5 Qxe5 23.Bxe5 Nxc4).

Another possibility is 21.Bxe5 Qxe5 22.d6, menacing 23.d7, but 22... Qd4+ 23.Qxd4 (else 23... Qxc4) 23... cxd4 24.d7 Nd6 and 25.Rxd4 is met with 25... Bc5.

The last line suggests 21.d6 Nxd6 (21... Nxc4 22.dxe7 Nxd2 23.exf8=Q+ Kxf8 24.Rxd2 + - [R vs P]) 22.Ba2 (22.Qxd6 Qxd6 23.Rxd6 Nxc4 White has lost a pawn and the bishop pair) with the threats Qxd6, Rfe1, Nd5, etc:

A) 22... Ndc4 23.Qe2 seems to win a piece (23... f6 24.Bxe5 followed by Qxc4+).

B) 22... Nec4 23.Bxd6 Nxd2 24.Bxd2 Nxf1 (24... Rfe8 25.Rxd2 + - [N vs P]) 25.Bxf8 + - [N vs P].

C) 22... Rad8 23.Nd5 Bxd2 (23... Qd7 24.Bxe5; 23... Qe6 24.Nxb4) 24.Nxe7+ Ke8 25.Rxd2 + - [2B vs N +P].

White to play (21.?) "Very Difficult"

First of all, I arrived at my solution by more or less a process of elimination. Not 21. Rfe1? Nxf3+, or 21. Rde1 Nxc4 22. Rxe7 Nxd2. Also the try 21. Qe2 (hoping for 21...f6?? 22. d6+) is well answered by 21...Nd6! (blockading the d-pawn) and neither 22. Bxe5 Nxc4 23. Qxc4 Qxe5 or 22. Qxe5 Qxe5 23. Bxe5 Nxc4 satisfies, and if 21. Qe2 Nd6 22. Ba2 Rae8 23. Rde1 f6! is now possible, and all of Black's problems are solved. So I thought, "What if we sacrifice a pawn so there is no blockade?"

21. d6! Nxd6

Clearly forced, otherwise Black loses the Ne5. If 21...Qxd6 simply 22. Qe2 wins the knight. If 21...Nxc4 22. dxe7 Nxd2 23. exf8=Q+ Kxf8 24. Rxd2 and White is up a rook.

22. Ba2!

Necessary, as 22. Qe2 Ndxc4 leaves Black ahead.

22...Rad8

Alternatives: 22...Nf5 23. Rde1 Rad8 24. Qf2 and the knight will fall; 22...c4 23. Nd5! Bc5+ (23...Bxd2 24. Nxe7+ and 25. Rxd2 wins a piece) 24. Kh1 Qe6 25. Bxe5! wins a piece since 25...Qxe5 26. Rfe1 Qf5 27. Ne7+ wins the queen.

23. Qe2! Rfe8

As 23...Nc6 24. Qxe7 Nxe7 25. Bxd6 wins a piece.

24. Nd5 Qd7

Or 24...Qe6 25. Nf6+, winning the queen.

<21. d6!!> White's strongest winning chance (+1.28 @ 21 depth).

The tempting 21. Qe2 is White's second best, but it's worth only a slight advantage (. Fritz's third choice is 21. Rde1 which also fizzles to only a slight advantage (0.59 @ 21 depth).

<21...Nxd6> Best and forced. Others lose decisively.

For example if 21...Qxd6 (other tries are worse), then 22. Qc1!

(not 22. Qxd6?? Nxd6 23. Ba2 Bxc3 24. bxc3 Ndc4! 25. Bxe5 Nxe5 26. f4! Ng4! 27. Rd7 with White's win dwindling to only a slight advantage)

22...Qb8 23.Nd5 Kh7 24. bg3! Ba5 25. Qe3 Nd6 26. Qxe5! Nf5 (26...Nxc4 27. Qe4 Qd8 28. Ne7 ) 27. Qxb8 Raxb8 28. Bxb8 (+6.46 @ 21 depth)

<22. Ba2> Until the search depth reaches 20, Fritz initially prefers 22. Bd5!? (+1.36 @ 21 depth). However, at 21 depth, 22. Ba2! (+1.45 @ 20 depth) is preferred.

<22...c4?> This is the losing move.

Black can complicate and leave the outcome in doubt with 22...Nd5 23. Rde1! Rad8 24. Bd5! Nxf3+ 25. Bxf3 Rxd2 26. Rxe7 Rxb2 27. Nd1! Rxh2! 28. Rxb7 (+1.29 @ 29 depth).

<23. Nd5!> (+3.50 @ 20/41 depth) Black's previous move overlooks this surprise Knight Fork, which exposes both Queens to attack but wins on the spot.

<23...Bc5+> Black's resistance is futile, but he still plays on for a few moves.

If 23...Bxd2, then 24. Nxe7+ Kh7 25. Rxd2 (+7.79 @ 2/45 depth) leaves White a piece up for an easy win.

<24. Kh1 Qe6 25. Bxe5!> (+4.36 @ 20 depth)

Black resigns as 25...Qxe5 26. Rfe1 wins with the threat of a royal fork after 26...Qf5 27. Ne7+ .