Top seed Amelie Mauresmo edged out Serena Williams 6-4, 0-6, 6-2 in a thrilling battle at the US Open to reach the quarter-finals on Monday.
Twice former champion Williams looked set for victory when she roared back from the loss of the first set but Mauresmo rallied to clinch a dramatic victory.
"I'm very excited," Mauresmo said.
"I'm pretty happy with the third set but let's forget (about the second). I'm glad I was able to really focus back into the match from the beginning of the third set."
The Frenchwoman dominated the early stages and took the first set but Williams ripped through the second set to level the match.
But after a cagey opening to the decider, Mauresmo broke in the sixth and eighth games, clinching victory with an angled backhand drop volley.
The world number one will play Russian Dinara Safina in the quarter-finals.
Safina beat Virginie Razzano of France 6-0, 7-5.
Third seed Maria Sharapova recovered from a slow start to beat China's Li Na 6-4, 6-2 to also reach the quarter-finals.
Li, the first Chinese woman ever to make the last 16 at Flushing Meadows, raced to a 4-1 lead but Sharapova hit back strongly to wrap up victory in 78 minutes.
World number 22 Li forced Sharapova into several uncharacteristic errors early on but once the Russian found her range, the result was never in doubt.
