My opinion is that Sidious wanted Windu to win. He raised his guard at exactly the wrong time to let Windu deliver the finishing attack. Windu did not use any complex tactics to defeat him. He merely hit him in a spot that and would have invariably stunned anyone struck by the move. Sidious wanted Windu to incapacitate him so he could beg in the corner for Anakin to see. The image of an old man being molested by a supposed ally was a crafty way to play on Anakin´s humility. Sidious sensed Anakin was coming. He decided to improvise a strategy, not certain that Anakin would have come to his aid of his own free will.
I fought on the battlefield. I retired to embrace a life of discovery and profit. I carve my own path in life and am better for it.