Japan's former world No. 4 Kei Nishikori reached the quarterfinals of the Atlanta Open on Thursday, beating China's Shang Juncheng 6-4, 7-6(3) in the second round of the ATP 250 tournament.
The 33-year-old, currently ranked 439th and making his first appearance on the ATP Tour since October 2021, broke his opponent's serve in the opening and seventh games to win the first set before prevailing from the second-set tiebreak against the 18-year-old, 156th-ranked Shang.
Nishikori beat 63rd-ranked Australian Jordan Thompson 7-6(5), 7-6(5) in the first round on Tuesday.
"This match was better than the first round," Nishikori said after reaching the last eight. "I went aggressive from early on with my forehand. I'm satisfied with my play."
Nishikori, who had his left knee taped for the match, won 40 percent of return points off Shang's first serve.
"I could hit my returns deep and surprised him many times," said Nishikori, who faces world No. 9 Taylor Fritz of the United States in the quarterfinals on Friday.
Nishikori underwent hip surgery in January 2022 and subsequently injured his right ankle while rehabilitating.
He won his comeback tournament in June at the Caribbean Open, an ATP Challenger Tour event in Puerto Rico, before playing in two more Challenger Tour events in the United States.