Djokovic strolls into last eight
Novak Djokovic had his first uncomfortable moments of the US Open but retained his status as the Mr Consistent of the grand slams.
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The world number one's 6-1 7-5 6-4 victory over German Philipp Kohlschreiber in oppressive heat and humidity sent him through to a 22nd consecutive grand slam quarter-final.
Not since the French Open in 2009 has he failed to reach the last eight at a slam - when coincidentally he was beaten by Kohlschreiber in the third round.
He is still 14 short of Roger Federer's all-time record but his level of play at the majors has been exceptional, the Serbian only failing to make the final in four of his last 16 slams.
"I'm very glad obviously that I had so many consecutive quarter-finals of grand slams," he said.
"It says that I do value these tournaments the most and try to always perform my best tennis in them. Obviously it motivates me for the future to continue that streak."
Djokovic is looking to make it five finals in a row at Flushing Meadows and add a second title to the one he won in 2011.
The man who beat him in 2012, Andy Murray, awaits in a heavyweight quarter-final that Djokovic certainly goes into as favourite.
The top seed has not dropped a set yet at Flushing Meadows, but came close against Kohlschreiber.
Having won the first five games and then the opening set in double-quick time, Djokovic became embroiled in a much closer tussle in the second.
Kohlschreiber had a point to take the set at 5-4 but Djokovic saved it with a nerveless cross-court pass and then broke immediately.
The Serbian is not normally a fan of hot and humid weather and looked very drained by the end of the match.
He said: "You can always work on your endurance but it's not possible always to feel at 100 per cent.
"Obviously in the match you go through times where you feel better, where you feel worse, depending on your emotional state, depending on the level of performance of your opponent, how much pressure he puts on you and so forth. It varies.
"It's important obviously in these particular conditions not to get carried away by frustration of the heat. And especially after long rallies to try to get an extra breath.
"I tried to focus on each point individually, because I knew that I definitely wanted to stay not too long there. Obviously when I won the second set I wanted to get the job done in three."
Third seed Stan Wawrinka reached the quarter-finals with a 7-5 4-6 7-6 (9/7) 6-2 victory over Spain's Tommy Robredo.
It is the fourth time in his last five grand slams that the Australian Open champion has made the last eight, but he did it the hard way.
After receiving treatment in the third set when he ended up in the stands after trying to chase down a backhand, the Swiss had to save two set points in the tie-break.
He and Robredo had words in the fourth set but by that point Wawrinka, who beat Murray in the quarters last year, was already firmly in control.
Kei Nishikori also booked his place in the quarter-finals after an epic encounter with fifth-seeded Canadian Milos Raonic which finished at 0226 in the morning local time - the joint latest finish in US Open history.
Nishikori, the 10th seed from Japan, looked on his way out as he trailed 2-1 heading into the fourth set but battled back to take the match 4-6 7-6 (7-4) 6-7 (6/8) 7-5 6-4 and set up a clash with Wawrinka.
The encounter lasted well over four hours but provided great entertainment for the sizeable crowd that stayed until the early hours to watch its completion.