Laura Robson
Robson crashes out of the US Open after a third round defeat. (Reuters)

Laura Robson is out the of the US Open after losing in straight sets to Li Na of China in their third round match at Flushing Meadows.

The Brit suffered a 6-2 7-5 defeat at the hands of her fifth seeded opponent in just one hour and 21 minutes as Li got her revenge on Robson, having lost to the Brit at the same competition 12 months ago at the Arthur Ashe Stadium.

Robson racked up 30 unforced errors, seven more than her Chinese opponent who impressively landed 11 aces - defining factors in the 19-year-old's loss. The British number one struggled to put any pressure on her opponent whatsoever and dropped her own concentration at crucial moments in the contest as Li capitalised on an underwhelming performance.

Li marched to a 4-1 lead in the opening set as she dominated the rallies before Robson provided a hint of resistance to close the gap to 5-2. It would prove to be short-lived however as Li sealed the first set in just under half an hour.

Robson returned for the second set looking sharper, getting off to a bright start to take the first three games of the set. But Li would not be discounted as she rapidly pulled things back to 3-3 to haul herself back into the set on serve.

The 19-year-old took the seventh game but the unforced errors that peppered her performance on Friday evening would prevent her from building on her confident start to the set, as she dropped serve in the 11th game as Li took a 6-5 advantage.

Robson, who had impressively defeated Caroline Garcia in the second round, was unable to break Li as she served another powerful ace to seal her win.

Li will take on former world No 1 Jelena Jankovic or Kurumi Nara from Japan for a place in the last eight.

"I was really happy how I was hitting on the court," the 2011 French Open winner told Sky Sports. "And I thought I served really well."

Despite her win, Li believes her coach Carlos Rodriguez will continue to drive her to improvement.

"He would think I can come even more to the net. I'm still young. I can do even more hard work."