01 Jan 09
You're right. 25. b5? was the blunder. 25. Qxa6 was the winning move.
To continue your line, I think that the best move for black would be 26. ...Re8. But after 27. c3 Re2 28.Bd4! he will be forced to either give up his bishop or lose almost all his pawns. Clearly a win for white.