It has to be Aayla Secura. I mean how could you not get distracted in the fight? Nobody could resist taking a peak at those blue boobs. And that's all she would need to cut you down, one quick glance and you're dead. They should have had her fight the Palpatine instead.
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I'd say Sidious. Windu is one of the greatest Jedi Lightsaber fighters, and Sidious could have easily soloed him. And if Clone Wars (TV series) is canon, Sidious destroyed Maul and Savage.