Personally, I think Palpatine let Mace win, but I think Mace came closer to actually wining then what was comfortable for Sidious.
Palpatine could force lightning Mace all he wanted too, but Mace had a lightsaber that could hold that energy, which we could see with Yoda, that yoda wasn't using his lightsaber and could see him get tired of containing the energy.
I think Palpatine was not a very proficient fighter with a Lightsaber, preferring to focus on his force powers.
In the same section with him and Yoda, he is throwing senate pod things at him, not engaging him, preferring to strike from a distance.
Yoda was like 875 years old at that time, but once he got the force flowing through him, well... It also plays a factor that he isn't a human.
Palpatine has got to be around 75-80 at that time, and because he is a human, his body has limitations at that age.
He can have the force flowing through him, but he can't have the extent of the force where he could fight Yoda and win.
Which is why he threw pod things at him.