Kvitova falls at US Open

New York - Wimbledon champion Petra Kvitova became the fifth top 10 seed to exit the US Open in the first week when she was knocked out by Serbian world number 145 Aleksandra Krunic on Saturday.

Third seeded Kvitova lost the third round tie 6-4, 6-4 to the pint-sized 21-year-old from Belgrade, who came through qualifying and had never won a match at a major before this year's event.

Kvitova joins second seed Simona Halep, fourth-seeded Agnieszka Radwanska, Angelique Kerber, the sixth seed, and eighth-seeded Ana Ivanovic in failing to make the fourth round.

The 24-year-old Kvitova dropped serve five times and committed 34 unforced errors against the 5ft 4in (1.63m) Krunic who divides her time between the pro tour and studying for a university economics degree.

"It was an honour to play on the same court as Petra, she's a great champion. I watched both her wins at Wimbledon," said Krunic.

"I wanted to be myself on court, play as long as possible. I didn't expect to win. I hoped to win a set."

Krunic said she tried not to think about nerves even as a 4-2 lead in the second set was swallowed up by Kvitova who pulled level at 4-4.

But the slender Serbian broke for 5-4 and claimed her famous win on a second match point when another Kvitova forehand sailed wide.

"On match point I thought 'Don't serve a double fault.' I just wanted to keep the ball in until she missed," added Krunic who will next face either former world number one Victoria Azarenka of Belarus or Russian Elena Vesnina for a quarter-final berth.

Kvitova said she was taken by surprise by her opponent's poise and power.

"I didn't really expect how she played so well. Suddenly she just pushed the ball very hard," said the Czech.

There were no such problems for men's top seed Novak Djokovic, the 2011 champion, who brushed aside America's Sam Querrey for the eighth time in nine meetings, with a 6-3, 6-2, 6-2 win taking the world number one into the fourth round at a major for the 22nd consecutive time.

"Sam is big server, very powerful. But he doesn't move that well so I wanted to keep him moving around the court, mix up the pace and get as many returns as possible back," said Djokovic after an 85-minute win which was never in doubt from the time he raced into a 5-0 lead in the first set.

Djokovic will next face John Isner, the last American left in the draw, if the 13th seed can beat Germany's Philipp Kohlschreiber.

Also going through to the last-16 for a third successive year was Canadian fifth seed Milos Raonic who beat Victor Estrella Burgos, the 34-year-old tournament debutant from the Dominican Republic, 7-6 (7/5), 7-6 (7/5), 7-6 (7/3).

He will face Japanese 10th seed Kei Nishikori who reached the fourth round for the first time since his 2008 debut with a 6-4, 6-2, 6-3 victory over Leonardo Mayer of Argentina.

Women's top seed Serena Williams faces her third successive American opponent in the shape of Uzbekistan-born left-hander Varvara Lepchenko.

The five-time champion is looking to claim her 75th match win at the US Open.

Australian Open champion Stan Wawrinka, the third seed, faces Slovenia's Blaz Kavcic, the world number 92, who has never defeated a top-10 opponent in 10 attempts.

Andy Murray, the 2012 champion, aims for a seventh appearance in the fourth round when he takes on Russia's Andrey Kuznetsov, who knocked world number five David Ferrer out of Wimbledon this year.

Results on Saturday from the sixth day of the US Open, the final Grand Slam tournament of 2014 (x denotes seeded player):

Men

Third round

Novak Djokovic (SRB x1) bt Sam Querrey (USA) 6-3, 6-2, 6-2
Kei Nishikori (JPN x10) bt Leonardo Mayer (ARG x23) 6-4, 6-2, 6-3
Milos Raonic (CAN x5) bt Victor Estrella (DOM) 7-6 (7/5), 7-6 (7/5), 7-6 (7/3)

Women

Third round
Flavia Pennetta (ITA x11) bt Nicole Gibbs (USA) 6-4, 6-0
Aleksandra Krunic (SRB) bt Petra Kvitova (CZE x3) 6-4, 6-4