Calculating Forcing Moves

GM Larry Christiansen (of ICC's Attack With LarryC column) is a renowned fierce attacker.

Here's what he once said about tactics and combinations.

He quotes,"One extremely important point I wish to emphasize is to always look at forcing moves.... As a player, I tended to calculate fairly deeply but I would often abandon a tactical possibility just when it seemed to lose its feel."

What Larry Christiansen means is that when you're about to embark on a dangerous combination, you should always try to calculate it to its very end.

Here's a game I played recently on FICS.

White in order to get over the misfortune, tried to castle his king into safety with the move 13. O-O and of course, this meant that this move was a case of out of the frying pan and into the fire.

It's Black to play.

a. Can you calculate how to take advantage of this situation?
b. How far did you calculate? Where did you stop?
c. What are White's responses to your possible moves?

In this case here, I calculated the above to its natural conclusion. So if you feel like giving this a go, Please stop reading now if you want to work this out for yourself.

----------- Answer below ---------------

I'm sure most of you would have found the immediate move
13.... Nxe3
14. fxe3 Qxe3+

Now here's the trick. What are White's responses?

A quick calculation reveals that
15. Kh1 loses a piece after
15.... Qxe2
16. Qxe2 Bxe2 so this line can be quickly discarded by White since Black will win.

But are there any possible responses?

15. Rf2 was the only other option.

Okay, the Rook defends e2 and blocks the check. The phrase "blocks the check" should now stir something in your head.

How do you make use of this pin?

15... Bc5! is the killer move. The rook is only defended once by the King so putting additional pressure on the pin makes sense.

Can White defend it? The only move left is:

16. Qe1 (White Queen has to defend the d2 Knight, e2 Knight and f2 Rook) (See 2nd diagram on right)

If you've calculated this far, can you now apply the correct combination?

16.... Bxe2 and now it's over. The rest of the game as follows and this is what happened:
17. c4 (White is paralyzsed as any other moves does not affect the outcome) Qxf2+
18. Qxf2 Bxf2+
19. Kxf2 Bh5 winning with a whole Rook up
White resigns

Surprising, all these moves are forced. And if you found this line (like I did), it's kind of amazing that you had actually calculated some 12 ply moves in all.