Former US Open champion Stan Wawrinka on Tuesday became the oldest man to win a match at the tournament since 40-year-old Jimmy Connors in 1992.Wawrinka, 38, earned his first win in New York in four years as he beat Japan's Yoshihito Nishioka 7-6 (7/5), 6-2, 6-4 in the opening round.

"I think I'm playing well. I'm not trying to compare from the past because it's never good idea to compare a few years ago what I was doing," said Wawrinka, who lifted the US Open trophy in 2016.

"But I'm happy with my level. I know where I am right now. I know I can beat some really good players. I can be really competitive. I'm moving well."

The Swiss goes on to play Argentine 30th seed Tomas Martin Etcheverry, who outlasted Finnish qualifier Otto Virtanen in a fifth-set tie-break.

Wawrinka has reached the quarterfinals or better on six occasions at Flushing Meadows, but his win over Nishioka was his first at the event since he lost to Daniil Medvedev in the last eight in 2019.

"Last few months have been almost better every week with more win, with more confidence, with what I'm doing," he said.

"Hopefully I can keep pushing myself and get some big results before the end of the year."

Wawrinka, a former world No 3, saw his ranking drop as low as 361 last year after a lengthy battle with injuries.

He returned to the top 100 in February and arrived at the US Open ranked 49th, nearing the final act of his career but unwilling to call time just yet.

"You also want to push yourself for the maximum, be the better player, best as possible. Of course you're going to have up and downs in the career, with some positive emotions when you win, with some tough ones when you lose," said Wawrinka.

"There's many kind of emotions. It's part of the beauty of the sport, I will say. That's also one of the main reason I keep going, is to get those emotions. Hopefully positive ones.

"To get the feeling that you get when you enter the court with so many people, when you play US Open, when you play the biggest tournaments in the world," he continued.

"I never forgot why I start playing tennis and what I was dreaming when I was young, is to play US Open, to play those Grand Slams, big tournaments, ATP tournaments, to be there.

"I'm happy I can still play at that level."