SHANGHAI -- Alexander Zverev beat Alexander Bublik 7-6 (6), 4-6, 7-6 (1) to reach the Shanghai Masters quarterfinals on Tuesday in his first match since securing the year-end No. 1 ranking.
Zverev saved three set points in the first-set tiebreaker and beat Bublik for only the second time in five career meetings.
"My ankle was acting up, unfortunately," Zverev said. "It was kind of understandable because I have been playing a lot of tennis, which is kind of a good sign because I have been playing well. I am starting to feel my body more and more but I am happy to get through."
Bublik led 20-15 in aces but also had eight double faults to Zverev's one.
On Monday after third-ranked Carlos Alcaraz lost, Zverev became assured of finishing the year at the top of the rankings.
Zverev is currently No. 2 but he will overtake top-ranked Jannik Sinner next month after the Italian ended his season due to right knee inflammation.
Zverev won the French Open and U.S. Open this year for his first two Grand Slam titles.
Zverev will next face Alex de Minaur, who has won their last two meetings - both at the Laver Cup.
De Minaur beat Karen Khachanov 6-3, 6-4.
Also, Arthur Gea defeated Jakub Mensik 7-6 (4), 6-4.