Japan's Kei Nishikori advanced to the second round of the U.S. Open men's singles on Monday after his opponent Marco Trungelliti retired hurt in the second set of their match.

The seventh-seeded Nishikori had a trouble-free start to his campaign for a first Grand Slam title as he took the opening set off Trungelliti 6-1, and was up 4-1 in the second set when the Argentine qualifier retired, 47 minutes into the match.

"What I want most right now is confidence," Nishikori said.

"I wanted to end the match with a convincing win. To be honest, I wanted to play longer to get my feel for the game back and enjoy the game-day nerves," he said.

Nishikori, ranked No. 7 in the world, is playing in his first tournament since crashing out of the second round of the Western and Southern Open, also known as the Cincinnati Masters, earlier this month.

The 29-year-old Japanese has posted his best Grand Slam performances at the hard-court major in New York, reaching the final in 2014 and advancing to the semifinals twice.

Last year, Nishikori was knocked out at the semifinal stage by Serbia's Novak Djokovic in straight sets. Djokovic went on to claim the men's title while Japan's Naomi Osaka won the women's singles crown.

Also in the men's singles on Monday, Nishikori's compatriot Yoshihito Nishioka booked his place in the second round by coming from a set down to beat his American opponent Marcos Giron 3-6, 6-4, 6-4, 6-4.

Top seed and world No. 1 Osaka will face No. 84 Anna Blinkova of Russia in her first-round match on Tuesday.

Read also...

Multiracial athletes sparking debate in Japan ahead of 2020 Games

Rui Hachimura gives Japan a taste of his newfound marketing clout

Olympics: Experts predict record 2020 medal haul, top-3 for Japan