Stosur ends Robson fairytale as Roddick earns Del Potro showdown

British teenage prodigy Laura Robson's remarkable run at the US Open was finally halted by Samantha Stosur - but the defending champion was made to work at Flushing Meadows.

Laura Robson shakes hands with Samantha Stosur after their US Open match in New York

NEW YORK// Defending champion Samantha Stosur squandered eight match points but finally subdued stubborn teen prodigy Laura Robson 6-4, 6-4 to reach the US Open quarter-finals.

Seventh-seeded Stosur advanced to a last-eight meeting with an opponent she has never defeated, World No. 1 Victoria Azarenka of Belarus, who ousted Georgia's Anna Tatishvili 6-2, 6-2.

Russian third seed Maria Sharapova, the 2006 winner, met compatriot Nadia Petrova for a last-eight berth with the winner to face French 11th seed Marion Bartoli, who upset fifth-seeded Czech left-hander Petra Kvitova, the 2011 Wimbledon winner, 1-6, 6-2, 6-0.

Stosur, Australia's first women's Grand Slam champion since 1980, eliminated Robson, the first British woman in the last 16 at the US Open since 1991.

"I'm playing really well," Stosur said. "I'm glad to get another match. I'm happy to be into the quarters again."

Stosur has lost all six career meetings with top seed Azarenka, never taking a set off the reigning Australian Open champion. Azarenka's most recent victory over Stosur came in last February's Doha final.

"There's a few things I've learned over those matches that I can put into play and have a much better match and hopefully a very good one," Stosur said.

"You have to be 100 per cent prepared as soon as you serve, have your game plan and stick to it."

British 18-year-old Robson had sent three-time US Open champion Kim Clijsters into retirement and 2011 French Open winner Li Na out of the event in the previous two rounds.

But the youngest woman in the world's top 100 finally faltered under the pressure of the reigning queen of the Flushing Meadows hardcourts.

"Definitely disappointed. I felt like I didn't play as well as I did in my last three matches," she said. "I just hit too many unforced errors."

Robson broke Stosur in the third game of the match but the Aussie broke back in the next game and seized command, breaking again to take the first set and jumping ahead 5-2 in the second before struggling to close out the triumph.

"I didn't do too much wrong on any of (my match points)," Stosur said. "Though it was disappointing not to have gotten it in one of those other two games, I still felt like I was in a good positions.

Retirement-bound Andy Roddick and Juan Martín del Potro booked a fourth-round showdown of former champions at the US Open with the American facing the emotional tension of his next loss being his last.

Roddick, the 2003 US Open winner, advanced with a 7-5, 7-6 (7/1), 4-6, 6-4 victory over Italy's 59th-ranked Fabio Fognini while Argentine seventh seed Del Potro, the 2009 winner, ousted countryman Leonardo Mayer 6-3, 7-5, 7-6 (11/9).

Three days and two matches after US 20th seed Roddick said he would bid farewell to tennis after the Flushing Meadows fortnight, the American produced an electric atmosphere Sunday at Arthur Ashe Stadium before his victory.

"The outpouring of support has been humbling. I appreciate all the support. I really do," Roddick told the crowd. "You guys have made it so special. I'm just enjoying it. I love this place. I love all of you and I'm having a blast."

Roddick, who turned 30 last Thursday, has fought to keep his emotions under control as he contemplates the end of his career while trying to play his best on the court where he won his only Grand Slam crown.

"I'm trying to keep my emotions together all the time while trying to appreciate this tournament," Roddick said. "I know each time I go warm up it might be my last time."

Roddick said not even a championship would change his mind about retirement.

"That would be a hell of an ending, though," Roddick said. "I would take that."

Del Potro, however, wants to pull the plug on Roddick's dream run and claim his second title on the New York hardcourts.

The South American's 2009 title is the only Grand Slam crown in the past 30 not won by World No. 1 Roger Federer, defending champion Novak Djokovic or injured Spanish star Rafael Nadal.

"I know it's special, this day for him, but I'm doing my job," he said. "I'll try to be focused on my match, doing my things, making my shots. The match is going to be very tough but if I play at a high level it will be tough for both players."