My point of view is that Mace won the lightsaber duel, it just happens that Sidious was able to turn the tables when Anakin arrived at the room. He manipulated the situation and took control of it, turned Anakin against the Jedi and took the chance he had to finish off Mace.
"Evil is a word used by the ignorant and the weak. The dark side is about survival. It's about unleashing your inner power. It glorifies the strength of the individual."