His problems, I believe, started here. His pieces were beginning to show a bit of incoordination, leaving d5 open for a ripe strike in a couple of moves. All I needed to do was solidify my c pawn.
7... Ng8e7 8. Nb1d2 O-O 9. h3 b6
Solidifying the c-pawn before pushing d5. Being able to push d5 before move 10 in the Sicilian was probably not the best for White in this situation.
10. Nd2c4 d5
The perfect timing. Advancing with a strike on the knight on c4, and if exd, Nxd5 and Black really opens up the game.
11. exd5 Ne7xd5
exd Nxd as planned.
12. Kg1h2
? Not a blunder, but definitely not an ideal move in the position.
12... Nd5f4
Going straight for the jugular, and White loses the Bishop pair for sure. I could have taken the e3 Bishop, but that would have allowed his f-pawn a chance to capture and open the file for his rook. I wanted to be sure his rook was closed off for a little while longer.
13. Nf3g1
? Again, not a blunder, but here's the thing. That knight never participates in the game. It just shuffles around in that back corner for the rest of the game, then finally gets pinned to the king and cannot block Black's last move of the game.
13... Nf4xe2
And White's bishop pair is lost. Now, Black's DS bishop is staring at the e5 pawn for now, but once the e5 pawn advances, that bishop will be a monster down the long dark diagonal.
14. Qd1xe2
Maybe not the best. Nxe2 with the idea of re-maneuvering the knight through g3 to e4 might have been a better option, but even that is a bit slow. However, Qxe2 is now easily met with Bf5, threatening to take on d3 and win a piece.
14... Bc8f5 15. Ng1f3
?? One of the first genuine blunders of the game. Black is clearly better here, but only positionally up until this point. It is here that Nf3 is easily met with Bxd3, putting Black a clear piece up, with much more space on the board and a very open game.