Novak Djokovic tames heat and Joao Sousa to make quarters

Djokovic did his part improving his perfect record in US Open fourth round contests to 11-0 leaving it to Federer, who will take on Australian John Millman in the late contest on Arthur Ashe Stadium court to give the fans what would be a hotly anticipated matchup.

A Federer v Djokovic clash would provide the perfect contest to propel the US Open into the second week, with the two champions having claimed seven titles at Flushing Meadows between them.

Sousa arrived at the season's final Grand Slam in dreadful form having lost his last seven matches but suddenly found his game on the Flushing Meadows hardcourts knocking off two seeded players, number 12 Pablo Carreno Busta and number 17 Lucas Pouille, on route to the last 16.

The first Portuguese player to reach the fourth round of any Grand Slam, the 68th ranked Sousa never looked a threat to progress any further as his magical U.S. Open run came to an end.

The biggest concern for Djokovic might well have been the conditions as the heat returned to New York after a few days of relief.

"I prefer not to talk about how difficult it was," Djokovic said of the heat after the match.

"We are blessed to play this sport and this is one of the biggest stages.

"You have a team to get you ready, but sometimes you just have to survive."

Through his opening round matches Djokovic and his play both suffered under a blazing sun and with temperatures once again nudging into the 90s Fahrenheit (32 Celsius), the extreme conditions took a toll on 31-year-old Serb.

The sixth seed went off court two sets and 2-1 up for a medical evaluation.

The 13-time Grand Slam winner had made easy work of the opening set, breaking Sousa twice, the second time to close out set.

Things grew tougher in the second as a sluggish Djokovic laboured before again clinching the set with a break.

As the temperatures rose so did the tempers, both players engaging in animated arguments with chair umpire James Keothavong over points.

The Serbian former world number one will face either John Millman or Roger Federer in the quarter-finals.