Azarenka, meanwhile, found herself in a completely different kind of tussle against

In some ways, the mismatch makes Errani's trip to the U.S. Open look that much more impressive. She was the finalist at the FrenchOpen on the slow red clay at Roland Garros, but her game held up on the quicker hard courts, too, and Williams, not fully pleased with her own play to this point, was complimentary.

"I definitely played better today," Williams said. "I played better than my other matches. And playing someone like her, you have to go better."

Azarenka, meanwhile, found herself in a completely different kind of tussle against this year's French Open champion.