He wouldnt have been able to.
Palpatine was bending his lightsaber with his force lightning. If he really wanted to, he would of blown Mace to dust. But that was a key moment in Anakin's fall.
I know Palpatine could have killed him easily, but I don't think Mace would have fallen to the Dark Side, had he won. But Palpatine was stalling for Anakin to arrive. I don't think he expected Mace Windu to be so powerful though. At least, that's what I got from that duel. Mace Windu had the advantage in the duel.
Because he's awesome.