Why didn't Haye fight like he did in the last round for the whole fight?

Haye doesn't have great stamina and wasn't going to risk punching himself out. Valuev is also the least talented HW belt holder maybe ever. He's just big but he's slow and lacks any power whatsoever.

I'd say the hand; he did seem to be pretty reliant on his left after the first couple of rounds. He firedthe right VERY sparingly, and it seemed only when he had a nice clear shot down the pipe. He also seemed to shake his hand a bit after he landed so he was definitely feeling something. I think he kind of went for broke in the 12th based on hurting Valuev; it was worth the risk at that point. Doing that a few round earlier may have blown the fight for him. Who knows, I was impressed with how he pulled it off, though.

Valuev's performance was a disgrace and Haye did what he had to do. Landed about 30 hard punches in the fight and take virtually nothing. Seeing the beast do the dance in the 12th was amazing.

Personally I think he was a little too wary of Valuev considering the man's total lack of an offense and just fought a bad fight. A very dangerous one too, leaving so many rounds close like he did with a well known beneficiary of multiple robberies - two of which having occurred in Germany - in there with him.