Stanislas Wawrinka
Wawrinka is in the third round after Wednesday's victory.Getty

Third seed Stanislas Wawrinka sealed his place in the third round of the US Open after victory over Thomaz Bellucci despite dropping a nervous third set.

The Australian champion was given a further scare when he went a break down in the fourth as his Brazilian opponent threatened to pull level but Wawrinka recovered to seal a 6-3 6-4 3-6 7-6 victory at the Arthur Ashe Stadium.

Grigor Dimitrov, then man who brought an end to Andy Murray's attempt to defend his Wimbledon crown earlier this summer, also enjoyed a second round victory on Wednesday. As he did when the two met in the first round at SW19, the 23-year-old Bulgarian made short work of American hopeful Ryan Harrison, sealing a 6-2 7-6 (7-4) 6-2 win in just over two hours.

Elsewhere in the men's singles, sixth seed Tomas Berdych eased past Australia's Lleyton Hewitt with a 6-3 6-4 6-3 straight sets victory in their first round clash.

There was another shock in the women's singles as fourth seed Agnieszka Radwanska's misery at the US Open continued as she fell to China's world no.39 Peng Shuai in straight sets. It was the latest in a series of premature exits for Radwanska, who has now failed to reach the quarter-finals in nine tournaments in New York.

American Sloane Stephens also suffered a surprise defeat as she was beaten by Johanna Larsson, despite being a set and 3-0 up against her Swedish opponent before crumbling.

2006 champion Maria Sharapova was also given a shock in her first set against world no.95 Alexandra Dulgheru, but the fifth seed turned it around in emphatic fashion to seal a 4-6 6-3 6-2 win.

After barely overcoming Robin Haase in his opening round, Andy Murray is back in action on Thursday. The British number one was beset by cramp as he struggled to find rhythm in the New York heat on Monday against the Dutchman and will be hoping to improve when he meets German qualifier Matthias Bachinger on Arthur Ashe Stadium in his evening match.