(CNN) -- Kim Clijsters' glittering singles career came to a surprise end on Wednesday, as British teenager Laura Robson recorded a shock 7-6 7-6 win in the second round of the U.S. Open.
Clijsters announced earlier this year she would retire for the second time following the season's closing grand slam in New York, as she wants to spend more time with her family.
Robson, who recently won silver in the mixed doubles at the London Olympics, is ranked 89th in the world and wasn't expected to pose much of a challenge to the three-time U.S. Open champion. However, the former world No. 1 struggled to find an answer to her 18-year-old opponent's impressive serve.
"I'm happy that in the last year and a half or even two years, it's been kind of up and down, and I'm happy that I stuck through it and I was able to kind of live a lot of these emotions that I've had in these 18 months or so. I'm proud of myself that I was able to do that," said Clijsters, who will play in the women's doubles and mixed doubles at Flushing Meadows.
The 29-year-old, now ranked 25th, has struggled with injury this year since reaching the semifinals of January's Australian Open, a tournament she won last year.
Robson was only nine years old when Clijsters last lost a match at the U.S. Open -- which she won for the first time in 2005 then again after her retirement in 2009 and 2010 before missing out with injury last year. Clijsters has 41 tour titles to her name, behind only the Williams sisters among still active players, while Robson has yet to claim her first tournament victory.
Robson will now face Chinese ninth seed Li Na, and Clijsters tipped the 2008 Wimbledon girls' champion as a future star.
"Physically if she gets better, even more explosive, then I think she's going to be a great player, and someone that I'll be keeping an eye on," she said.
World No. 1 Victoria Azarenka and third seed Maria Sharapova breezed through their second-round matches, as did defending champion Samantha Stosur.
Azarenka defeated another Belgian, 133rd-ranked Kirsten Flipkens, taking only 27 minutes to record a 6-2 6-2 victory and set up a last-32 clash with Chinese 28th seed Zheng Jie
"I think it was another good performance today," the Australian Open champion said.
"It wasn't as easy maybe as the score was, but I think I played well. I always take it match by match no matter where it is, whatever my ranking is. I have been doing it for pretty much my whole career."
Sharapova, the 2006 U.S. Open winner, steamrolled over Spain's Lourdes Dominguez Lino 6-0 6-1 in 54 minutes.
The French Open champion, the highest-paid sportswoman in the world, will next face someone at the other end of the financial scale -- American amateur Mallory Burdette.
Burdette eliminated Czech doubles specialist Lucie Hradecka, who ranked 69th is 183 places higher in the WTA list, and would have pocketed $65,000 so far if she could accept it.
However, she would forfeit her place at Stanford University by becoming a professional athlete.
"I have already checked the amateur box, so if I know correctly, you can't go back once the tournament starts. So it's done," said the 21-year-old, whose only other grand slam appearance was a first-round defeat in New York six years ago.
"At this point, I'm used to giving the money up, I think the money goes straight back to the tournaments if I don't declare it, so they probably love me at this point!"
Burdette was encouraged to sample the pro tour by Stanford tennis coach Lele Forood.
"I wasn't sure if I even wanted to play tennis as a career, but Lele was so supportive and encouraged me to give it a shot," she explained.
"I really want to be a psychiatrist. So I was interested in med school. I would have finished up my degree and I would have gone to some type of program where I could take all my pre-med requirements and then hopefully go to med school.
"I had given that a lot of thought at the beginning of the summer and I was preparing for that. I still am in a lot of ways, but my success this summer has kind of taken me in a different path a little bit. So I think my focus will be a little bit different when I go back to school."
Fifth seed Petra Kvitova also went through to the third round, beating former world No. 11 Alize Cornet 6-4 6-4 to earn a clash with another French player, 90th-ranked Pauline Parmentier.
The Czech, who won her maiden grand slam last year at Wimbledon, took just 78 minutes to beat Cornet, now ranked 50th.
Seventh seed Stosur will next play Uzbekistan-born American Varvara Lepchenko, with the Australian beating Romania's Edina Gallovits-Hall 6-3 6-0.
Stosur has had mixed fortunes since winning the title a year ago, losing in the first round of her home grand slam, reaching the last four at the French Open and exiting in the second round at Wimbledon and the first hurdle at the Olympics.
Kvitova's 15th-seeded compatriot Lucie Safarova also went through, beating Canadian Aleksandra Wozniak 6-3 4-6 6-2.
She will next face Russian 19th seed Nadia Petrova, who ended the hopes of Romania's world No. 53 Simona Halep.