Sara Errani of Italy serves to compatriot Flavia Pennetta at the US Open tennis championships in New York, Aug 29, 2013. [Photo/Agencies]

Sara Errani became the highest seed to be knocked out of this year's US Open when she suffered a surprise 6-3 6-1 loss to Flavia Pennetta on Thursday.

Errani, seeded fourth for the women's singles, was sent packing after just 71 minutes by her fellow Italian in a second round match at Arthur Ashe Stadium.

A semi-finalist at Flushing Meadows last year, Errani was looming as a contender this year and appeared to be in great form after doling out a rare double-bagel win in her opening match against Australia's Olivia Rogowska in under an hour.

Errani will now focus her attention on the doubles where she and her countrywoman Roberta Vinci will defend the title they won last year.

Vinci fared better in her second round singles match on Thursday with the 10th seed defeating Lucie Safarova 4-6 6-1 6-2.

Flavia Pennetta of Italy serves to compatriot Sara Errani at the US Open tennis championships in New York, Aug 29, 2013. [Photo/Agencies]