Returning former world No. 4 Kei Nishikori came from behind to reach the quarterfinals of the Caribbean Open tennis tournament in Puerto Rico on Thursday, beating Mitchell Krueger of the United States 4-6, 6-3, 6-2 in the second round.

The 33-year-old Japanese, who underwent hip surgery in January last year before hurting his right ankle while rehabilitating, on Tuesday played his first competitive match since October 2021, securing a first-round win at the ATP Challenger Tour event.

Following a slow start against Krueger, Nishikori picked up in the second set when he secured a vital break back in the eighth game en route to taking the match to the final set.

Nishikori jumped to a 4-0 lead in the decider before wrapping up the win in just under 2 hours, 20 minutes.

"I couldn't play with patience at the start, but I had everything my way in the second half of the match," said Nishikori, who admitted to feeling the effect of his long layoff.

"I have this unbelievable tiredness that is close to the one I had after playing a Grand Slam semifinal," he said. "I'll do my best again in the next game."

Japan's Kei Nishikori hits a serve against Mitchell Krueger of the United States during a second-round match at the Caribbean Open in Palmas del Mar, Puerto Rico, on June 15, 2023. (Kyodo)