Carlos Alcaraz showed no sign of being hampered by an ankle injury as he beat Belgium's Zizou Bergs 6-4, 6-3 on Saturday to reach the Japan Open quarter-finals.
The world number one hurt himself two days earlier in his opening match in Tokyo, crumpling to the ground before playing on with his ankle heavily strapped.
The Spaniard was left sweating on his fitness, but he showed no evidence of discomfort as he returned to the court to beat world number 45 Bergs in front of an adoring Japanese crowd.
Alcaraz got the job done in an hour and 20 minutes and will face American Brandon Nakashima in the next round on Sunday.
Alcaraz took to the court with white strapping visible underneath the sock on his left ankle.
He did not appear to be restricted in his movement, but he limped briefly after chasing a shot that won Bergs a break early in the first set.
Alcaraz is playing in Japan for the first time and he delighted the crowd with a series of leaping forehand winners, claiming the first set despite having his service broken twice.
He raced into an early lead in the second set, but Bergs made him work hard for the victory with a gritty performance.
Alcaraz sealed the deal with a thumping forehand at the net that Bergs could not return into play.