8 ...f5!? was unusual in this exact position. If then 9 exf5 Bxf5 10 Bd3 Be6 is reasonable for Black. Nunn expected 10 ...fxg3 11 hxg3 Nf6 but the aggressive young French grandmaster chucked in a pawn to create activity down the f file.
14 Be2? looks strong but it turns out that Black really can sacrifice. If 15 Bxf2 Rxf2 16 Kxf2 Bh4+ 17 Kg2 Qg5+ 18 Bg4 Ne5 (not 18 ...Bxg4? 19 Qd5+) 19 h3 h5! is very dangerous so Nunn, as intended, played 15 Qd5+! He had missed 16 ...Nb4! but after it saw all the way to the diagram though not Nataf's spectacular 24th move.
If 17 Qd1 Rxf2 18 Kxf2 Bh4+ 19 Kg2 Qg5+ 20 Bg4 Bxg4 now wins easily since the black knight prevents 21 Qd5; while 17 Qd4 Rxf2 18 Kxf2 Bh4+ 19 Kf3 Bh3!! cutting off the king's retreat leads to a win after 20 Nd5 Qg5 21 Nf4 Rf8 22 Qxd6 Rxf4+ 23 Qxf4 Bg2+ 24 Ke3 Qc5+ 25 Kd2 Bg5; and 17 Qd2 Rxf2 18 Kxf2 Bg5! forces a transposition.
If 19 Ke3 g6 20 Qf3 Qg5+ 21 Qf4 Qc5+ 22 Kd2 Bg5! wins and 20 Qh6? Bg5 traps her immediately. Nataf threw in another piece with 21 ...Bh3+! and after 22 Qxh3 Rxf8+ Nunn couldn't return the queen in view of 23 Qf3 Rxf3+ 24 Bxf3 Qe3 25 Kg2 Qf2+ 26 Kh3 Qxf3+ 27 Kxh4 h6!
In the diagram 24 ...Rxf3+? 25 Kg2 is simply bad while 24 ...Qxf3+? 25 Kg1 Qe3+ 26 Kg2 Qf3+ is only perpetual check. Instead, Nataf quietly brought in the knight with 24 ...Nd3!!.
Then if 25 Re1 Rxf3+ 26 Kg2 Nf4+! 27 Qxf4 Qf2 mate or 25 Kg2 Qxf3+ 26 Kg1 Nf4 etc. 25 Nd5 was desperation and Black could have won immediately with 25 ...Rxf3+ 26 Kg2 Qe2+ 27 Kg1 g5! though the line he chose was quite good enough..
A truly superb game!
White: John Nunn
Black: Igor Nataf