Petra Kvitova became the latest top seed to fall at the U.S. Open on Saturday.
American Alison Riske provided the surprising upset with a 6-3, 6-0 rout of the seventh-seeded Czech in third-round action. Kvitova, the 2011 Wimbledon champ, became the second top seed to bow out in the first week as fourth- seeded Sara Errani lost in the second round.
Kvitova hasn't fared too well at Flushing Meadows, with a pair of fourth-round results her best finishes in now six trips to the USTA National Tennis Center.
Riske, whose lone previous U.S. Open ended in a first-round loss in 2011, gained a measure of revenge after losing to Kvitova in the second round of last week's tune-up event in New Haven. Kvitova needed three sets to dispose of the 23-year-old Pittsburgh native last week and never found a rhythm on Saturday.
Kvitova committed seven double-faults in just eight service games and had 27 unforced errors overall, compared to just seven from Riske.
Another early winner Saturday was 21st-seeded Simona Halep. The Romanian blasted 14th-seeded Russian Maria Kirilenko, 6-1, 6-0, to keep her brilliant summer going.
Halep has captured four titles since a first-round loss at the French Open, winning in Nuremburg, Den Bosch, Budapest and last week at New Haven. She beat Kvitova in last weekend's final and her lone three losses since Roland Garros have come against Li Na in the second round at Wimbledon, Flavia Pennetta in the second round at Bastad and Serena Williams in the Cincinnati quarterfinals.
She'll get another crack at Pennetta in the fourth round, as the unseeded Italian followed her second-round upset of Errani with a 7-5, 6-1 win over 2004 U.S. Open champ Svetlana Kuznetsova on Saturday.
Pennetta, a three-time U.S. Open quarterfinalist, hasn't dropped a set in her three matches this week.