Slovakia's Dominika Cibulkova became the first woman into the US Open quarter-finals with victory over former champion Svetlana Kuznetsova.
At 45th in the world, Cibulkova is the lowest ranked player remaining in the draw, but the 21-year-old shrugged off her poor summer form to secure a 7-5 7-6 (7/4) victory on Arthur Ashe Stadium.
Cibulkova had not won back-to-back matches in six tournaments since Wimbledon before arriving in New York, but won her first two matches at Flushing Meadows in three sets before dropping just one game in beating Lourdes Dominguez Lino in the third round.
Against Kuznetsova she took the opening set when her Russian opponent served a double fault on set point at 5-6 down, but Kuznetsova hit back to move into a 3-1 lead in the second.
However, Cibulkova won the next four games in a row and held two match points at 5-3 and 40-15 before succumbing to nerves, Kuznetsova winning four points in a row to get back on serve.
A tie-break was required and Kuznetsova's 10th double fault of the match helped Cibulkova into a 5-1 lead, the young right-hander this time holding her nerve to close out the match.
Cibulkova will face the winner of the fourth-round match between top seed Caroline Wozniacki and former champion Maria Sharapova in the quarter-finals.
Estonia's Kaia Kanepi also advanced to the quarter-finals after an extraordinary comeback against 15th seed Yanina Wickmayer of Belgium.
Kanepi, who knocked fourth seed Jelena Jankovic out in the previous round, lost the opening set without winning a game but stormed back to win 0-6 7-6 (7/2) 6-1 in two hours 21 minutes.
The 31st seed, who also reached the quarter-finals of Wimbledon this year, made 46 unforced errors in the match, but crucially only six in the decider as she set up a last-eight clash with the unseeded Andrea Petkovic or seventh seed Vera Zvonareva, who contest the first night match on Monday evening.
