But Black went greedy and moved the Rook to a3, trying to gobble up Queen side pawns.

Well, yes, fatal error (and nice checkmate), but in this position with also only about one minute (and after berserking no increment for me) left on the clock, situation was already completely hopeless, so that I actually don't consider this move to be my main mistake in this game, which I think was move 23, Ne2??, one of my typical blackouts in fast games.