Novak Djokovic came through a battle with the elements and apparent physical issues to reach the quarter-final of the US Open with a straight-sets win over Joao Sousa.

A prospective last-eight clash with Roger Federer was the reward on offer for the Wimbledon champion, but his fourth-round clash proved more difficult than the 6-3 6-4 6-3 scoreline suggests. 

While Sousa lacked the weaponry and the consistency to trouble Djokovic, the searing heat at Flushing Meadows, the behaviour of the crowd and umpire James Keothavong all left him perturbed at various junctures.

But Djokovic rediscovered his fluency in the final set after a concerning break for a medical timeout and won nine of the last 11 points to dispatch Sousa and set up a mouth-watering quarter-final, providing Federer can overcome John Millman.

A stunning backhand pass gave Djokovic the break in the third game of the match, and a routine first set was sealed with a break to love as Sousa sent down a double fault.

Yet his progress in the second set was far from serene, Djokovic committing a double fault of his own to give Sousa a love break in the third game and showing visible irritation after members of the crowd applauded him missing an overhead.

That only served to fire up Djokovic, though, and he immediately broke back and went on to clinch the second thanks to a pair of errant Sousa groundstrokes, but only after he displayed furher signs of discontent, hurrying a ball boy after receiving a time violation during a tricky service game.

Concern was apparent in the Djokovic box in the opening stages of the third, which saw him stop during a point when 40-0 down only for Sousa to subsequently hit long with the court at his mercy.

However, if Djokovic was understandably lacking in energy he did not show it during a spirited debate with Keothavong after losing a game in which he claimed Sousa stopped deliberately to challenge during a rally before then continuing and winning the point.

Djokovic's subsequent off-court medical evaluation was only brief, and he was rejuvenated in the final games, breaking to love, ironically with a successful overhead, to go 5-3 up. Sousa's challenge came to an end a game later as he fired long on Djokovic's second match point.

STATISTICAL BREAKDOWN
Djokovic [6] bt Sousa 6-3 6-4 6-3

WINNERS/UNFORCED ERRORS
Djokovic – 23/18
Sousa – 21/28

ACES/DOUBLE FAULTS
Djokovic – 9/1
Sousa – 4/5

BREAK POINTS WON
Djokovic – 5/6
Sousa – 1/1

FIRST SERVE PERCENTAGE
Djokovic – 67
Sousa – 54

PERCENTAGE OF POINTS WON ON FIRST/SECOND SERVE
Djokovic – 78/56
Sousa – 70/41

TOTAL POINTS
Djokovic – 88
Sousa – 67