Victoria Duval, 17, dropped the first set to Australian Samantha Stosur, but the young American battled back to take the final two on Tuesday, pulling the biggest upset of the U. S. Open so far.

Duval overcame 35 unforced errors for her first ever Grand Slam victory, 5-7, 6-4, 6-4. The former U. S. Open champion was on the ropes in the third set, with Duval serving for the match up 5-4. But Stosur fought off two match points before Duval’s forehand winner buried the Aussie.

At times, Duval certainly showed her age and inexperience, but she was able to overcome both for easily the biggest win of her career.