New York, Aug 30 : Novak Djokovic kept his quest for a historic 25th Grand Slam title alive on Friday, overcoming a brief lower back issue to defeat unseeded Briton Cameron Norrie 6-4, 6-7(4), 6-2, 6-3 and book his place in the fourth round of the U.S. Open.

Under the lights at Arthur Ashe Stadium, the 38-year-old showcased his trademark resilience to become the oldest man to reach the last 16 at Flushing Meadows since Jimmy Connors achieved the same feat in 1991.

Already the all-time leader in Grand Slam titles (24) and match wins (395), Djokovic added another milestone to his storied career by surpassing Roger Federer for the most hardcourt wins at the majors, claiming his 192nd victory. The four-time U.S. Open champion also extended his perfect record against Norrie to 7-0.

"I guess coming into the match, any match, you really want to win in straight sets without any drama and just ease through, but that's not possible," said Djokovic.

"My team wants me to suffer on the court so I can get some more minutes spent in match play. It's good that I get tested. I hadn't played any matches since Wimbledon and it's been for us quite a long time, five to six weeks.

"I'm still trying to find my groove and my rhythm on court," he added.

Djokovic quickly turned up the pressure on Norrie, breaking for a 4-3 lead with a forehand winner. He then fired the ninth of his 18 aces in the next game to firmly consolidate his advantage.

"I think it was probably the best serving performance of the tournament," Djokovic said.

"So of course I'm glad. It's probably one of the most, if not the most important shot in the game. Yeah, I'm glad how I executed that shot."

After taking a 5-4 lead in the first set, Novak Djokovic began feeling the effects of a back issue and briefly left the court for treatment before returning to close out the set. He needed more medical attention early in the second set, with his serve speed briefly dropping.

Despite this, he battled through a tight tiebreak that Norrie won. The Brit broke early in the third, but Djokovic responded with three straight games and even silenced a disruptive fan. Regaining full control, Djokovic closed out the third and dominated the fourth to seal the win and set up a clash with Jan-Lennard Struff.

/IANS