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Roger Federer has won in New York on five previous occasions

US Open Venue: Flushing Meadows, New York Dates: 28 Aug-10 Sept BBC coverage: Live radio and text commentary on selected matches every day.

Roger Federer was in clinical mood as he saw off Spain's Feliciano Lopez in straight sets to join Rafael Nadal in the US Open fourth round.

The third seed, who came through five-set matches in the first two rounds, beat 35-year-old Lopez 6-3 6-3 7-5.

Five-time champion Federer, 36, goes on to face Germany's Philipp Kohlschreiber in the last 16.

"I'm really excited how I feel after two five-setters," the 19-time Grand Slam champion said.

"It was clearly nice to go up two sets to love for a change. Feels different from there."

Top seed Nadal earlier beat Argentina's Leonardo Mayer 6-7 (3-7) 6-3 6-1 6-4 in three hours and 16 minutes.

With heavy rain halting play on the outside courts in the early evening, the action on Arthur Ashe Stadium stretched to almost 15 hours across the day.

Federer and Lopez did not get under way in the night session until 21:40 local time (02:40 BST) - almost three hours later than scheduled - and Madison Keys' 2-6 6-4 6-1 win over Elena Vesnina ended at 01:46 local time.

'I can finally focus on playing tennis'

Saturday's night session began with the oldest match-up at the US Open since 40-year-old Jimmy Connors played 32-year-old Ivan Lendl in 1992.

Federer looked sharp, showing no sign of the back issue that disrupted his build-up to the tournament, and had been in his thoughts during his first-round match in New York.

The timing that was still absent in round two had returned for the most part - with just four backhand errors - and, one poor service game in the third set apart, he dispatched 13th seed Lopez efficiently.

"I needed to get over the fear of the back issue, especially in that first match, the first set," said Federer. "Then I think the wobble I had in the second round was due to my preparation.

"I think now I'm just trusting my movement better. My serve is there. My mind is there. I can finally focus on playing tennis and not so much about the past."

Early pressure told with a break in game six and the first set followed after just 25 minutes.

With almost 80% of the points played in under four strokes, it suited the attacking, first-strike intent that has marked Federer's game during this stellar year.

A wayward Lopez volley saw the Swiss move ahead in the second and with 59 minutes on the clock he was two sets up.

The third was more testing as Lopez, trying for a first win over Federer in 13 attempts, took advantage of a loose service game to recover an early deficit.

He could not extend the Australian Open and Wimbledon champion into a fourth set, however, with Federer breaking serve in game 12 to clinch victory after one hour and 46 minutes.