Samantha Stosur is out of the US Open after suffering a straight-sets fourth-round loss to Flavia Pennetta.

The Italian has been a career-long nemesis of Stosur’s and defeated Australia’s last singles hope 6-4 6-4 on Monday to improve her head-to-head record to 7-0 over the 2011 champion.

Pennetta, seeded 26th, is through to her fifth quarter-final in New York and next plays either Czech fifth seed Petra Kvitova or Sydney-born Brit Johanna Konta on Wednesday for a spot in the last four.