The Chinese contingent enjoyed a perfect start at the US Open on Monday, with Zhang Zhizhen, Wang Xiyu, Wang Xinyu and Zhu Lin all notching first-round victories in New York.

After crashing out at the first hurdle at Wimbledon, Zhang returned to winning ways at the majors with a gritty five-set victory over American JJ Wolf in the men's draw.

The 26-year-old Zhang took a two-set lead before Wolf battled back to tie the match, with Zhang ultimately prevailing against the world No 45 7-5, 7-5, 6-7 (5), 4-6, 6-3.

At 4 hours and 29 minutes, the epic encounter proved to be the longest match of the day.

Zhang has enjoyed a fruitful 2023, becoming the first Chinese men's player in the Open era to reach the quarterfinals at an ATP 1000 tournament and advancing to the third round at the French Open.

Monday's victory marked another significant breakthrough for Zhang — his first five-set win at a Grand Slam.

"Finally I've won a five-setter! I lost all of them before," said the delighted 26-year-old, who added that he was finding the hard courts of Flushing Meadows challenging to adapt to.

"I lost in the first round last year, so I don't have much experience here. It's different than clay. I think the overall ball speed here this year is not as fast as last year," he said.

Zhang will take on last year's runner-up Casper Ruud in the second round. Ruud, the fifth seed, dug deep to battle past Emilio Nava of the United States, 7-6 (5), 3-6, 6-4, 7-6 (5).

Zhang shouldn't be too daunted by Ruud after producing an encouraging performance in a four-set loss to the Norwegian at this year's French Open.

"My opponent in the next round knows my style and I know about him," Zhang said of Ruud. "So I'll go back to the practice court and prepare well."

In the women's draw, Wang Xiyu displayed similar resolve to Zhang, defeating world No 76 Viktoria Hruncakova of Slovakia, 4-6, 6-3, 7-6 (6).

Wang Xiyu will next face Bernarda Pera of the US, who produced one of Monday's upsets by knocking out Russian 16th seed Veronika Kudermetova.

Wang Xinyu advanced with a 6-3,6-4 triumph over American Katie Volynets, ranked no 124. Wang Xinyu, ranked 53rd, will next take on Sara Sorribes Tormo of Spain, who overcame Ukraine's Anhelina Kalinina.

Zhu Lin also enjoyed a relatively straightforward passage to round two, beating Egypt's world No 33 Mayar Sherif 6-3, 7-5.

Zhu will next face 18th seed Victoria Azarenka of Belarus. Azarenka conceded just three games in total as she cruised past Frenchwoman Fiona Ferro.

Novak savors return

Novak Djokovic is back at the US Open and will now be back at No 1 in the rankings.

Djokovic made a winning return after missing the tournament last year, rolling to a 6-0, 6-2, 6-3 victory over Alexandre Muller on Monday night.

The 23-time Grand Slam champion had to wait through Coco Gauff's three-set victory to open the night session at Arthur Ashe Stadium, followed by an opening-night ceremony marking 50 years of equal prize money at the US Open.

"Well, I knew it was going to be a late night for me, late start of the match," Djokovic said. "Nevertheless, I mean, I was excited to go out on the court. I didn't care if I started after midnight because I was looking forward to this moment for a few years, to be out on the biggest stadium in our sport, the loudest stadium in our sport, playing the night session."

Djokovic was not allowed to travel to the US last year because he is not vaccinated against COVID-19.

Monday's contest was his first match at Flushing Meadows since falling to Daniil Medvedev in the 2021 final, a loss that prevented the Serbian from completing the first calendar-year Grand Slam in men's tennis since 1969.

Djokovic improved to 17-0 in first-round matches at the US Open and assured he will regain the No 1 ranking on Sept 11.

Because he couldn't play last year and had no rankings points to defend, Djokovic needed to only reach the second round to guarantee he would take top spot back from Carlos Alcaraz. It will be Djokovic's 390th week atop the rankings, extending his own record.