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.
The Australian seventh seed advanced to a last-eight meeting with either World No. 1 Victoria Azarenka of Belarus or Georgia's Anna Tatishvili, who were set to meet in a later night match at Arthur Ashe Stadium.
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.
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.
"I'm playing really well. 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.
Russian third seed Maria Sharapova, the 2006 winner, faced 19th-seeded compatriot Nadia Petrova for a quarter-final berth. The winner would meet either Czech fifth seed Petra Kvitova or French 11th seed Marion Bartoli.