The fourth seed lost 6-3, 6-4 to Chinese world number 39 Peng Shuai.

Radwanska, whose career Grand Slam high point came when she reached the Wimbledon final in 2012, has not made it past the fourth round at Flushing Meadows in nine straight attempts.

"I didn't play bad today," said Radwanska.

"I think it was just her day.

"Of course I could do something different maybe or try something else, but I really tried my best and I was fighting until the end.

"I just couldn't do it."

There was also a surprise defeat for Sloane Stephens of the United States.

The 21st seed lost 5-7, 6-4, 6-2 to Sweden's Johanna Larsson.

She was a set and 3-0 up in the second before her game fell apart.

Elsewhere in the women's draw, 2006 US Open champion Maria Sharapova survived a scare after dropping the first set.

The Russian soon turned things around to beat world number 95 Alexandra Dulgheru of Romania 4-6, 6-3, 6-2.

Two-time champion Venus Williams is also through to the third round after a 6-1, 6-4 win over Swiss Timea Bacsinszky.

And number two seed Simona Halep of Romania made light work of her opponent, beating Jana Cepelova of Slovakia 6-2, 6-1.

Australian Open champion Stan Wawrinka dropped the third set before regaining the initiative to progress to the third round ©Getty Images



In the men's draw, Swiss third seed Stan Wawrinka survived a mid-match lapse.

The Australian Open champion was two sets up when he dropped the third.

But he secured a four sets win over Tomasz Bellucci of Brazil on a tiebreak, coming out on top 6-3, 6-4, 3-6, 7-6.

A tasty clash between Tomas Berdych of the Czech Republic and Australian Leyton Hewitt proved to be a case of one-way traffic.

Berdych, the number six seed, won it 6-3, 6-4, 6-3.

Meanwhile, Marcos Baghdatis of Cyprus retired with an injury in the second set of his match against 14th seed Marin Cilic of Croatia, having been down 6-3, 3-1.

Tomorrow will see the top seeds in the men's and women's draws, Serbian Novak Djokovic and American Serena Williams, in second round action.