Camila Giorgi came from behind to upset No. 6 seed Carolina Wozniacki 4-6, 6-4, 6-3 at the US Open on Saturday night.
Giorgi came up with 45 winners, compared with only 13 for Wozniacki.
Giorgi faces Roberta Vinci in the Round of 16, but Giorgi didn't pull Saturday's only upset. Wild card Alison Riske shocked No. 7 seed Petra Kvitova 6-3, 6-0 to reach the fourth round for the first time in her career.
Riske won the last eight games against the seventh-seeded Czech, who was in bed with a fever the day before.
"I've got a new confidence in myself," Riske said through tears in an on-court interview. "I believe that I belong here."
It's quite a turnaround for Riske, who lost to Kvitova last week at the New Haven Open 7-6 (7-5), 4-6, 6-3.
Riske was 0-5 at major tournaments this year before Wimbledon, but has gone 5-1 since. She will next meet Daniela Hantuchova, who defeated Julia Glushko 3-6, 7-5, 7-6.
In other women's action, two of the top seeds were forced to rally past unranked opponents. No. 13 seed Ana Ivanovic needed three sets to beat American Christina McHale 4-6, 7-5, 6-4, while second-seeded Victoria Azarenka beat Alize Cornet 6-7, 6-3, 6-2.
Ivanovic and Azarenka will meet in the Round of 16 on Monday.