Zhang, ranked 67th in the world, had come through another five-setter to beat American JJ Wolf in his opener and showed similar resolve against world number five Ruud en route to securing the biggest victory of his career.

"Last year at the US Open, I can say it was a bad memory. This year is a little bit different," said Zhang, who squandered seven match points in his 2022 opener before losing to Tim van Rijthoven in five sets.

He was blanked by Ruud in the fourth sets but said he never lost hope.

"I believed in myself. If not, the fifth set was going to be a different result," he told reporters. "I was a little bit tired for few days already. I had some sort of pain, whatever. I don't spend so much energy. I try to be calm for whole match.

"At the end of the match, finished the last point, I didn't really celebrate like, not super happy. But I was happy inside, it just didn't show."

Zhang, who will play Australian Rinky Hijikata in the third round, has a number of tennis 'firsts' for China where the sport has largely been dominated by women in the modern era.

In May, he became the first man from his country to win a main draw match at the French Open in 86 years when his Serbian opponent Dusan Lajovic retired due to illness.

After beating Argentine Agustin Tirante in the second round at Roland Garros he was then dumped out of the tournament by Ruud, so Wednesday's victory comes as sweet revenge.

Last October, Zhang became the first Chinese man to break into the top 100 in the world rankings and he also became the first to reach the quarter-finals of an ATP Masters 1000 tournament at the Madrid Open this year.

Zhang is now on the verge of cracking the top 50 and said interest in men's tennis was increasing back home.

"More and more people are watching. More people are trying to play tennis. At least in Shanghai, now we get more courts, we have more people to play," he added.

"Especially in the last year, we broke into the top 100, then Wu Yibing got into the US Open third round. Now even better."