Novak Djokovic of Serbia serves to American Sam Querrey at the US Open on Saturday (US time) in New York City. Photo: AFP

 

Novak Djokovic and Andy Murray stayed on course for a mouth­watering US Open quarterfinal showdown on Saturday (US time) as five-time women's champion Serena Williams stood alone as the last singles title hope for the US.

But as the heavyweights of the sport eased into the fourth round, the ­women's draw was blown open again when Wimbledon champion Petra Kvitova became the fifth top-10 seed to exit in the first week.

Kvitova's misery was shared by American tennis after John Isner and Sam Querrey were both knocked out in the third round, which left the hosts still without a men's Grand Slam champion since Andy Roddick triumphed in New York in 2003.

Djokovic, the 2011 champion, brushed aside Querrey for the eighth time in nine meetings, with a 6-3, 6-2, 6-2 win taking the world No.1 into the fourth round at a major for the 22nd consecutive time.

Djokovic's victory was never in doubt from the time he raced into a 5-0 lead in the first set.

Wimbledon ­champion and seven-time major winner Djokovic will next face Germany's Philipp Kohlschreiber who ended US hopes with a 7-6 (7/4), 4-6, 7-6 (7/2), 7-6 (7/4) win over Isner despite the American 13th seed firing 42 aces and 77 winners.

Williams racked up her 75th victory at the US Open when she eased past her third successive American ­compatriot, Uzbekistan-­born left-hander Varvara Lepchenko, 6-3, 6-3 and will ­tackle tough Estonian Kaia Kanepi for a quarterfinal berth.

Williams is aiming to become just the second ­woman after Chris Evert in the 1970s to win three New York titles in succession.

Murray, the 2012 champion, hit 47 winners in a 6-1, 7-5, 4-6, 6-2 victory over Russia's Andrey Kuznetsov, the world No.96, to book a seventh appearance in the fourth round and goes on to face French ninth seed Jo-Wilfried ­Tsonga who beat Pablo Carreno-­Busta of Spain 6-4, 6-4, 6-4.

Third-seeded Stan Wawrinka reached the fourth round without hitting a ball when Slovenian opponent Blaz Kavcic withdrew with a right foot injury. That took the number of retirements and walkovers at this year's US Open to 10 in the men's event and two in the women's.

Wawrinka next faces 16th-seeded Spaniard Tommy Robredo, a 3-6, 6-3, 7-6 (7/4), 6-3 winner over Australian Nick Kyrgios, who had shocked Rafael Nadal in the fourth round at Wimbledon.

Women's third seed Kvitova lost her third-round tie 6-4, 6-4 to pint-sized Serbian, 21-year-old Aleksandra Krunic, who came through qualifying.

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.