Routine victory for Roger Federer in US Open

Federer, who came into the tournament nursing a suspect back, took an off-court medical time-out at the end of the second set but did not appear hampered as he claimed a 6-4 6-2 7-5 victory.

The Wimbledon champion is through to a 12th quarter-final at Flushing Meadows where he will face Juan Martin del Potro in a rematch of the 2009 final following the Argentinian's epic comeback to beat Dominic Thiem.

Explaining the reason for his departure from the court, Federer said: " I just needed a bit of a rub on my back, my bottom and I didn't want to do it on court. I wanted to get it done as soon as possible so Philipp wouldn't have to wait.

"It was a great match for me against Philipp, he can be very tough but I protected my serve very well and that helped me tonight."

The third seed is now looking forward to a first meeting in New York against Del Potro since 2009, when the Argentinian won his only grand slam title.

Federer said: "It's great to see him back on tour. He's had a rough ride for a lot of the years. To see him back, happy and winning and beating the best players in the world is wonderful for our sport.

"To play him here after our epic final in 2009 is great and I think we're both looking forward to it, or at least I am."

Having been well below his best in five-set wins over Frances Tiafoe and Mikhail Youzhny in the first two rounds, Federer appeared to have shrugged off concerns over his form by easing past Feliciano Lopez.

If Federer could have handpicked his draw, he may well have selected these very opponents given his one-sided record against the latter three.

After beating Youzhny for the 17th time and Lopez for the 13th time, Federer took a 11-0 head-to-head record into his clash with Kohlschreiber.

The German has a fine one-handed backhand and a consistent record of reaching the second week at grand slams, but he could find nothing to hurt Federer.

With the cheers audible from Grandstand as Del Potro neared his remarkable victory, proceedings on Arthur Ashe were much more routine.

Federer broke Kohlschreiber three times in the first two sets and did not face a break point himself all match.

The third set looked like it might go to a tie-break but Federer broke in the 11th game and then clinched the victory with his 39th winner after an hour and 50 minutes.