Chinese ninth seed Li Na was knocked out of the US Open in the third round on Friday, losing 6-4, 6-7 (5/7), 6-2 to Britain's Laura Robson, who had beaten triple champion Kim Clijsters in the previous round.
Robson becomes the first British woman to make the last 16 in New York since Jo Durie in 1991 and will face defending champion Samantha Stosur of Australia for a place in the quarter-finals.
"It was really tough," said Robson, who said she will maintain her positive approach when she faces Stosur. "I have nothing to fear."
The 18-year-old Robson, the youngest player in the world top 100 and the 2008 Wimbledon junior champion, showed few signs of nerves as she swept into the fourth round of a major for the first time.
Her win over 2011 French Open champion Li was her first victory against a top-10 player and was her second successive victory over a Grand Slam title winner after sending four-time major champion Clijsters into retirement on Wednesday.
Defeat meant it's the first time since 2008 that Li has not reached at least the quarter-finals at any Slam during a season.
In a topsy-turvy encounter on the Armstrong court, Robson and Li exchanged five breaks of serve in the opening set before the Briton clinched the crucial break in the 10th game.
Li, who came into the tournament on the back of a title in Cincinnati, her first since her landmark French Open win in 2011, and a runner-up spot in Montreal broke to lead 1-0 in the second set.
But left-hander Robson hit straight back for 1-1 before Li went on to take the tiebreak.
Li fought off three break points in the third game of the decider and two more in the fifth before gutsy Robson deservedly broke to lead 3-2.
Robson backed it up with a hold and another confident break to lead 5-2 and then wrapped up the tie when Li went long with a forehand.