Alexander Zverev was forced to dig deep in beating Quentin Halys in three sets at the Shanghai Masters on Sunday as he closes in on the world number one ranking.
The German top seed belatedly saw off the Frenchman 6-4, 6-7 (8/10), 6-3 to reach the last 16, despite moving a little uncomfortably at the end.
"He plays unbelievably aggressive and serves incredibly," Zverev, himself one of the biggest servers on tour, said of his beaten opponent.
"This year I have been picking my tournaments and places where I want to peak, I did not do that early in my career.
"It paid off, I won two Grand Slams and reached the Wimbledon final."
Zverev cut a frustrated figure at times, barking at his corner even as he clinched the first set against the 48th-ranked Halys in 38 minutes.
The second set was much closer, going with serve and taking them into the tie-break.
Zverev unleashed a delicious backhand down the line to avoid going down 6-4 in the tie-break, but then squandered a match point when he shanked a forehand return.
A second match point came and went, and Halys took full advantage to force a deciding set courtesy of an overhead smash.
The third was poised for another battle, but Zverev broke for 2-0 and behind his reliable serve powered home for victory.
Zverev, the world number two, is an imminent threat to Jannik Sinner's number one ranking.
The US Open and French Open winner has never topped the rankings.
The Italian Sinner is not playing in Shanghai because of injury, opening the door for the 29-year-old Zverev to usurp him.
World number three Carlos Alcaraz is in action on Monday.
The Spaniard faces Belgium's Zizou Bergs in the third round.
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