Prize money row Janko Tipsarevic into US Open last-eight

Serb eighth seed Janko Tipsarevic, fresh from a Twitter stir where he reignited the equal prize money row at the US Open, reached his second successive quarter-final at Flushing Meadows on Wednesday.

Tipsarevic brushed past German 19th seed Philipp Kohlschreiber 6-3, 7-6 (7/5), 6-2 and goes on to face Spanish fourth seed David Ferrer for a place in the semi-finals.

Just days after criticising the entertainment value of women's tennis, and questioning why the likes of Maria Sharapova and Serena Williams didn't play five sets, Tipsarevic played out his match in front of just a smattering of fans on Grandstand.

The 28-year-old, who led 5-2 in the first set overnight before his fourth-round match fell victim to the heavy New York rain, enjoyed his best Grand Slam performance at the US Open in 2011 when he reached the last eight.

But a knee injury forced him to retire in the fourth set against compatriot and eventual champion Novak Djokovic.

Kohlschreiber, whose previous match against John Isner ended at a record-equalling late finish of 2:26 a.m. on Monday morning, committed 53 unforced errors.

Djokovic, the second seed, is bidding to reach the quarter-finals for the sixth straight year and his 13th successive last-eight at a major, when he continues against Swiss 18th seed Stanislas Wawrinka.

The world number two was leading 2-0 overnight when his match was halted.

Djokovic has a 10-2 record against Wawrinka with the Swiss player not having defeated the world number two in six years.

The Serb, who is also the Australian Open champion, has only dropped 14 games in three rounds in New York this year.

Wawrinka is bidding to reach the quarter-finals for the second time, having made the last eight in 2010 where he was beaten by Russia's Mikhail Youzhny.

The 27-year-old Swiss has lost 18 matches in a row against top-10 players.

Djokovic or Wawrinka will go on to face either 2009 champion Juan Martin Del Potro, the Argentine seventh seed, or 2003 winner Andy Roddick for a place in the final.

Roddick, 30, was just a point ahead in the first set tie-break when play was halted overnight.

Del Potro -- whose New York triumph victory in 2009 was the only time in the last 30 majors that either Djokovic, Roger Federer or Rafael Nadal wasn't champion -- is trying to make the last eight for the first time since that win.

The big Argentine has won three of his four meetings with Roddick, but the American came out on top in their most recent clash, in the semi-finals on hardcourt in Memphis in 2011.

Roddick's 2003 victory in New York remains was the last time an American man won a Grand Slam title.

On a bumper day of action at Flushing Meadows, top seed Federer was taking on Czech sixth seed Tomas Berdych for a place in the semi-finals.

Federer, bidding to become the first six-time champion in 87 years and make a ninth straight semi-final in New York, will meet either British third seed Andy Murray or Marin Cilic, the 12th-seeded Croat, for a place in the final.

Federer beat Murray in the 2008 US Open final.