Ah a similar theory to mine that Sidious was not dueling with Mace properly, it would make sense to me that Sidious is supposed to be far more powerful then any of the other Jedi/ Sith, Because first off (And I'm going by the films as I only have heard of the characters from the comics etc not read any of the comics, seen some in games) The jedi should not be as powerful as a very developed Sith because by their nature their strength lies elsewhere, the draw of the darkside is the power it offers, Jedi have power of a different kind, also among the Sith Sidious is the current Sith Lord, and therefore should be considerably stronger then the other Sith, so that means he should be the strongest around in the current era, hence how he goes on to create a empire, and finally is not beaten by a traditional sense, back to the power of a different kind possessed by Jedi.

Hmm, I see this Mace beating Sidious in that duel spoken of alot, loads of youtube videos have it in the comments, I can understand why ppl think it, also it could be the correct interpretation, however, I felt when I watched the movie, and before I noticed ppl saying this, my initial interpretation watching was that Darth Sidious the Sith Lord was using Mace as a means to luring Anakin to the dark side, by making him choose between the jedi and padme, he was just playing with mace using enough dueling skills to make Mace put effort in so that he could take the fall and appear weak and in need to anakin, putting anakin in a position where he had to either let mace kill Sidious and Padme would die, or stop mace and she would live. I always thought from this interpretation I had made that this ment Sidious was significantly more powerful then mace since he was willing to lose his lightsabre and risk mace striking him, so therefore he must be strong enough in the force that mace posed no danger to him even without his lightsabre. but maybe I just interpreted the scene wrongly.