Petra Kvitova upset by Jamie Hampton of US at Roland Garros

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Jamie Hampton of the United States stunned 2011 Wimbledon champion Petra Kvitova of the Czech Republic 6-1, 7-6 (7) at the French Open on Saturday to reach a Grand Slam fourth round for the first time.

The 54th-ranked Hampton, who lives in Auburn, Ala., needed only 13 winners because the seventh-seeded Kvitova finished with 33 unforced errors, 15 more than the American. Kvitova was a French Open semifinalist in 2012.

Hampton joined 67th-ranked Bethanie Mattek-Sands and No. 17-seeded Sloane Stephens, who both won earlier Saturday, and No. 1 Serena Williams, who won Friday, in the fourth round. That gives the U.S. its most women at this stage at Roland Garros since 2004, when there were also four.

Five U.S. women made it to the fourth round in Paris in 2003.