drukenknight: My book by Howson (200 Fianchetto Traps) claims something like this is a known trap. Usually white will play e5 to avoid this sort of thing. He cited a game Mileika/Tal that is not in the data base. But Korchnoi pulls this trap off, by juggling his move order just a subtle little bit.
Black for his part usually will capture exd5 as soon as the chance is presented, then he follows w/ Re8. Here Korchnoi reversed those two moves.
By deferring the capture ...exd5 for one move, black waits as first whites goes Qc2 then Be2, then black breaks open the center, when both those pieces are there.
White usually does not play Q to c2 right off but waits (plays Be2 first) and usually gets in 10 e5 before playing the Q to c2. This is usually where white dilemma lies, at his 10th move his Q is not already there but still on d1.
In most cases, white will recapture w/ cxd5 and then will be able to play e5 on a later move because there is no other pressure on the e pawn (there is no R on e8) so the N on c3 holds this pawn vs the N on f6.
But here, as soon as 9...exd5 10 cxd5 black already had the R on e8 and so 10...Nxd4 followed the pawn recapture immediately.
Here black delayed the initial pawn capture to get his Re8 and the white Q went out to c2 ahead of time. Just a subtle difference and whites whole game is thrown off.
sac: 10...Nxe4
c8-f5.
