Gatti also tried that for the next 5 rounds after that. We all know what happened then.
I don't see Gatti winning the 1st rnd even without the knockdown.
He landed nothing significant at all. Nothing.
I've watched this fight around 30 times.
He lands maybe one decent left jab in the entire round and nothing else.
But Floyd pounced on him with some decent flurries around 5 or 6 times in the first.
If anything, the round could've been a draw. But giving that round to Gatti based on the fact that he survived is a gift.

What I'm saying is, Floyd will beat you to the punch on the outside every time.
It's hard to hit Floyd flush when he can see your punches coming.
Zab still gets nailed with good shots on the outside against slower fighters.
So what's he gonna do when he faces Floyd's speed.
Zab may be able to survive by staying on the outside, but if he wants to win it he'll need to sacrifice himself and crowd him. Hoping to catch him with a wide shot when he's in close and Floyd can't see it coming.