New York - Defending champion Samantha Stosur squandered eight match points but finally subdued stubborn British teen prodigy Laura Robson 6-4, 6-4 in 98 minutes on Sunday 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 percent prepared as soon as you serve, have your game plan and stick to it."
Robson, an 18-year-old from England ranked 89th, 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.
"If you're not doing the wrong things on those points, you can't get too down on yourself."
Robson held and broke and threatened to hold again to level the match before Stosur struck, firing a forehand winner that Robson sent wide to end the fight.
"She had some good points. She made some great shots," Stosur said.
Azarenka, who won her first Grand Slam title at this year's Australian Open, reached her first US Open quarter-final in her seventh appearance, having now cracked the last eight in every Grand Slam event.
It will be Azarenka's fifth quarter-final in the past seven Slams. She can ensure she stays atop the rankings next week by reaching the final, but first she must maintain her mastery of Stosur.
"She's very dangerous," Azarenka said. "What she did here last year was absolutely amazing. It's definitely going to be a very difficult match.
"As defending champion she's going to be really motivated. I'm motivated as well. It's my first quarter-final at the US Open and I'm really looking forward to it."
Bartoli reached her first US Open quarter-final in her 11th attempt, denying Kvitova her first trip to the last eight after she had been the only player to reach the quarter-finals in the year's three prior Slams.
"I'm speechless and that doesn't happen very often," Bartoli said. "It has been my dream to play well in New York. It's one of the best matches of my season. I was moving so well. I was seeing so well on the court. I'm so happy."
Results from the seventh day of the US Open on Sunday (x denotes seeding):
David Ferrer (ESP x4) bt Lleyton Hewitt (AUS) 7-6 (11/9), 4-6, 6-3, 6-0
Novak Djokovic (SRB x2) bt Julien Benneteau (FRA x31) 6-3, 6-2, 6-2
Andy Roddick (USA x20) bt Fabio Fognini (ITA) 7-5, 7-6 (7/1), 4-6, 6-4
Stanislas Wawrinka (SUI x18) bt Alexandr Dolgopolov (UKR x14) 6-4, 6-4, 6-2
Juan Martin Del Potro (ARG x7) bt Leonardo Mayer (ARG) 6-3, 7-5, 7-6 (11/9)
Richard Gasquet (FRA x13) bt Steve Johnson (USA) 7-6 (7/4), 6-2, 6-3
Janko Tipsarevic (SRB x8) bt Grega Zemlja (SLO) 6-4, 6-3, 7-5
Philipp Kohlschreiber (GER x19) bt John Isner (USA x9) 6-4, 3-6, 4-6, 6-3, 6-4
Samantha Stosur (AUS x7) bt Laura Robson (GBR) 6-4, 6-4
Victoria Azarenka (BLR x1) bt Anna Tatishvili (GEO) 6-2, 6-2
Marion Bartoli (FRA x11) bt Petra Kvitova (CZE x5) 1-6, 6-2, 6-0
Maria Sharapova (RUS x3) bt Nadia Petrova (RUS x19) 6-1, 4-6, 6-4