In game three, Kamsky played the following Anti-Marshall:
1.e4 e5 2.Nf3 Nc6 3.Bb5 a6 4.Ba4 Nf6 5.O-O b5 6.Bb3 Be7 7.Te1 O-O 8.h3 Bb7 9.c3
9.d3 is the usual continuation nowadays, but 9.c3 has of course been known for a long time, too. The reason nobody is playing 9.c3 anymore, is that Black can now play his intended gambit anyway:
9..d5 10.exd5 Nxd5 11.d3
Accepting the gambit here with 11.Nxe5 seems too risky, because of 11..Nxe5 12.Rxe5 Nf4. However, this system is completely harmless anyway, Black should have already achieved equality at this point.
In fact Black doesn't even have to defend his pawn. He could just play 11..Qd7, because after 12.Nxe5 Nxe5 13.Rxe5 Bf6 he has excellent compensation. But 11..Qd6 is fine, too.
12.Nbd2 Rad8 13.Ne4 Qd7
The queen could also go to g6, here, and Black should have nothing to worry.
Now Bacrot rapidly lost the thread of the game. After 14..b4 I don't see any problems for Black.
15.axb5 axb5 16.d4
Now Black could try 16..f5, with the idea of playing ..e4. White's knights do look a bit dangerous after 17.Neg5 e4 18.Nh4, but after 18..g6 they cannot be supported by the white queen, and Black should be fine.
16..exd4 17.cxd4 f6?
But this move is really bad. 17..Nf6 was probably still ok for Black. After
18.Nc3 Ncb4 19.Qe2
Kamsky won a pawn and later the game.