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Five-time US Open winner Roger Federer took another straight-sets step at the 2015 championships with a 6-3 6-4 6-4 third-round victory over Philipp Kohlschreiber at Flushing Meadows.

Third seed Andy Murray also enjoyed a straight-forward win after two earlier battles to advance with a 6-3 6-2 7-5 victory over Brazilian Thomaz Bellucci.

Murray, who won his first major at the 2012 US Open a year before winning Wimbledon, had fought back from two sets down to beat France's Adrian Mannarino in the second round after needing four sets to beat Australian Nick Kyrgios in his opening match.

Federer, meanwhile, lost his serve for the first time in the tournament as Kohlschreiber broke him twice in the 93-minute match, but the 34-year-old Swiss stayed in command with five service breaks of his own to improve his career record to 10-0 against the German.

"I think I won the big points today," said Federer, who cashed in five of eight break point chances.

"I served well when I had to at the end."

Next up for Federer in the round-of-16 is big-serving John Isner, who advanced when Czech Jiri Vesely retired due to a neck injury when trailing 6-3 6-4.

The 13th-seeded American hammered 21 aces and 46 winners past Vesely in the abbreviated match.

The evergreen Federer, the grand slam king with 17 titles but none since the 2012 Wimbledon, has been brutally efficient with his own serve during a strong season and an impressive build-up to the US Open.

He was a finalist at Wimbledon in July and has captured five ATP titles this year, including last month's Cincinnati Masters, where he defeated world number one Novak Djokovic in the final.

Isner stands between Federer and a place in the quarter-finals [AP]

Elsewhere, French Open champion Stan Wawrinka powered his way to a third successive straight sets win, beating Belgian Ruben Bemelmans 6-3 7-6(5) 6-4 to reach the fourth round.

The aggressive Swiss fifth seed belted 41 winners at Louis Armstrong Stadium to make up for 32 unforced errors against Bemelmans, who was appearing in the third round of a grand slam for the first time.

Wawrinka, who won his maiden grand slam at last year's Australian Open, will meet American Donald Young, who battled back to beat Serbian Viktor Troicki after losing the first two sets, for a berth in the quarter-finals.

Results: 

13-John Isner (US) beat Jiri Vesely (Czech Republic) 6-3 6-4 (Vesely retired)
2-Roger Federer (Switzerland) beat 29-Philipp Kohlschreiber (Germany) 6-3 6-4 6-4
6-Tomas Berdych (Czech Republic) beat 31-Guillermo Garcia-Lopez (Spain) 6-7(2) 7-6(7) 6-3 6-3
12-Richard Gasquet (France) beat 24-Bernard Tomic (Australia) 6-4 6-3 6-1
15-Kevin Anderson (South Africa) beat 20-Dominic Thiem (Austria) 6-3 7-6(3) 7-6(3)
5-Stanislas Wawrinka (Switzerland) beat Ruben Bemelmans (Belgium) 6-3 7-6(5) 6-4
Donald Young (US) beat 22-Viktor Troicki (Serbia) 4-6 0-6 7-6(3) 6-2 6-4

Source: Reuters