PARIS, June 1 (Reuters) - America's Jamie Hampton upset seventh seed Petra Kvitova in the French Open on Saturday as four American women made it through to the last 16 of a grand slam for the first time since 2004.
Hampton won 6-1 7-6(7) to join top seed Serena Williams, Sloane Stephens and Bethanie Mattek-Sands in the fourth round.
The last time four players from the U.S. reached the same stage was at the U.S. Open in 2004 when Williams was joined by her sister Venus, Jennifer Capriati and Lindsey Davenport.
"It's impressive, huh?," Hampton said about America's succeful quartet. "We have got a unique group I think between Serena, obviously the best player in the world, and Bethanie, Sloane, and myself.
"Three different players with very unique games, it's cool."
Czech Kvitova, Wimbledon champion in 2011 and French Open semi-finalist last year, came into Roland Garros on the back of some poor claycourt results and was lost for words after.
"I did a lot of mistakes and I really didn't know what was happening on the court," she said.
The charismatic Mattek-Sands, known for her frequently outrageous outfits, came through her third round clash against Paula Ormaechea 4-6 6-1 6-3, while Stephens beat New Zealand's Marina Erakovic 6-4 6-7(5) 6-3.
"I'm so happy that U.S. tennis is coming on strong," Mattek-Sands said.
"I think there are a lot of young guns coming up that will be dangerous. To have 13 women in the main draw here at the French Open, more than any other country, is awesome. I'm proud." (Reporting by Toby Davis; editing by Martyn Herman)