Novak Djokovic appeared to struggle with the heat again at the US Open but came through an intense clash with Joao Sousa in straight sets to reach the quarter-finals.
Djokovic took a long bathroom break after the second set, much to Sousa’s annoyance, and then went off court again early in the third set after calling for the doctor.
But the sixth seed did not face too many hairy moments in a 6-3 6-4 6-3 victory that took exactly two hours.
Djokovic said: “I’m very happy to get this one done in straight sets. It was much more difficult than the score indicated. Credit to Joao for fighting, he brought a lot of intensity on the court.
“It was very tough conditions, especially the first hour and a half. We are putting in all the work but sometimes you just have to survive.”
The extreme heat policy was again in action, with temperatures climbing over 30C and significant humidity, meaning a 10-minute break between the third and fourth sets, although this match did not get that far.
After a relatively comfortable first set, Djokovic found himself in trouble at the start of the second as Sousa, the first Portuguese player ever to reach the fourth round of a grand slam, broke for a 2-1 lead.
The 13-time grand slam champion hit straight back and went on to take the set but was clearly not enjoying himself in the heat, although his struggles were not as severe as during his first-round clash with Marton Fucsovics.
Sousa, a fiery presence, took exception to Djokovic’s lengthy bathroom break, and was then left sitting alone on court while his opponent consulted the doctor, but ultimately he could not find the shots to hurt him where it mattered.
Djokovic will face the winner of the Monday night clash between Roger Federer and John Millman, while also through to the last eight is Japan's Kei Nishikori.
The 21st seed defeated Philipp Kohlschreiber 6-3 6-2 7-5 and could next face a rematch of the 2014 final, which he lost to Marin Cilic.
Nishikori missed this tournament last year and the Australian Open in January because of a wrist injury and dropped down to the second-tier Challenger Tour to begin his path back.
He said: “I was playing one match at a time because I didn’t have any confidence and I was still worried about my wrist.
“The clay-court season was great then first time going to the quarter-finals in Wimbledon. It’s going well this year.”
