Kei Nishikori secured a spot in the third round of the U.S. Open when France's Gael Monfils retired with an injury in the second set of their second-round match on Thursday.
World No. 19 Nishikori was leading 6-2, 5-4 when his 39th-ranked opponent and 2016 U.S. Open semifinalist stopped night-session play at Louis Armstrong Stadium because of an injured right wrist.
Monfils resumed play after Nishikori's reflex volley hit his wrist and he called for a trainer, but eventually retired after dropping serve in the ninth game.
"I feel bad about Monfils' retirement," 2014 runner-up Nishikori said.
"But the good news is, I'm playing well. My condition is back and so is my confidence. (The next match) will be a tough one," he said.
Nishikori meets world No. 13 Diego Schwartzman in the third round. Nishikori is 2-0 against the 26-year-old Argentine.
Earlier in the day, in women's action, Naomi Osaka beat Julia Glushko of Israel 6-2, 6-0 in just 50 minutes to advance to the third round of the U.S. Open for the third year in a row.
"I didn't play so well at the baseline but my serves and returns were consistent," said the 20th-seeded Osaka, who won 10 consecutive games after the contest was leveled 2-2 in the first set.
"I did better than I did in the first round. I used to have emotional ups and downs during matches, but my main goal right now is to stay focused throughout the match."
Osaka, ranked 19th in the world, will next face Aliaksandra Sasnovich of Belarus, ranked 33rd.
In the women's doubles, the Japanese duo of Miyu Kato and Makoto Ninomiya suffered a straight-sets defeat to the Britain-U.S. pair of Naomi Broady and Danielle Collins, falling 6-3, 6-4 in a first-round match.