After killing Mace and the rest of the Jedi, Anakin walks in. Palpatine: I told you Anakin, I had to do it because they were trying to kill me. Anakin: Ok, I don't care about Mace anyways. Palpatine: Every Jedi including the kids and Obi-wan should all be destroyed. Anakin: Ok my master. Palpatine: I'll execute order 66 because the Senate will do anything I say anyways without proof. As you can see, if Palpatine could have done that in the first place THEN Palpatine could've done that way before THIS STAGED DUEL. Palpatine didn't have an off day. He KNOWS HE HAS TO LOSE.