Novak Djokovic enjoyed a reassuring 6-2 6-4 win against American Tennys Sandgren to advance to the Western & Southern Open quarter-finals on Tuesday.

The world No.1 seemed unphased by the neck pain that forced him to pull out of his doubles opener on Sunday and struggle against qualifier Ricardas Berankis in his singles second round on Monday.

But he was clinical in his clash with Sandgren, winning 84 per cent of his first-serve points and swatting away all four break points he faced.

Djokovic was also unshakeable up front, winning all 11/11 net points.

“I’m pleasantly surprised with the way I recovered and felt today, just overall physically, but also with the neck specifically,” said the 33-year-old Djokovic.

“I’m as closest to painless neck as I can be, just maybe five to 10 per cent more and that’s it. I’m feeling very good.”

The victory extended Djokovic’s flawless winning streak this season to 20 matches, and his next opponent Germany’s Jan-Lennard Struff predicts the Serb is looking to go unbeaten in this coronavirus-interrupted season.

“It’s crazy, just crazy,” Struff said of Djokovic’s record. “But the more you win, there is always a chance that you lose at some point. Maybe he has the aim to go undefeated in this short season. You never know what happens.”

Struff, who is one of just five players to take a set off Djokovic in 2020, made the quarter-finals in New York by ousting No.7 seed David Goffin 6-4 3-6 6-4.

Defending champion Daniil Medvedev, the No.3 seed, eased past Aljaz Bedene 6-3 6-3 and will face Spanish No.8 seed Roberto Bautista Agut for a place in the final four.