NEW YORK - Defending US Open champion Aryna Sabalenka was given an early test before she moved into the second round while Emma Raducanu won her first match at the Grand Slam since her 2021 triumph as the tournament began a day earlier than usual on Sunday.

Under the new extended 15-day format, first-round singles action will be contested from Sunday to Tuesday, rather than two days as in previous years, spreading out the star attractions and allowing access for another 70,000-odd spectators.

Sabalenka was among the marquee names on the opening day's schedule and the Belarusian fed off the vocal Arthur Ashe crowd to overcome determined Swiss Rebeka Masarova 7-5 6-1 and move into the next round.

"When I won that first set and you cheered for me, I got goosebumps," said Sabalenka, who will take on Russia's Polina Kudermetova in the second round on Wednesday.

"Your support means a lot to me, thank you for coming. It was an amazing atmosphere."

Novak Djokovic, the record 24-times Grand Slam singles champion, headlines the evening schedule on the main showcourt against American Learner Tien and he will be followed by 2024 finalist Jessica Pegula, who plays Egypt's Mayar Sherif.

Italian Jasmine Paolini kicks off the later programme on Louis Armstrong Stadium against Australian qualifier Destanee Aiava, followed by the 2021 champion and 13th seed Daniil Medvedev, who faces France's Benjamin Bonzi.

Compelling wins

Earlier, the extra crop of local ticketholders witnessed compelling wins from 2024 finalist Taylor Fritz, who beat compatriot Emilio Nava 7-5 6-2 6-3, and 2023 semifinalist Ben Shelton, who beat Peru's qualifier Ignacio Buse 6-3 6-2 6-4.

Fourth seed Fritz and the sixth seed Shelton have emerged as two of the brightest hopes to end a 22-year US men's drought at their domestic major, as their women's counterparts have long carried the torch for American tennis.

Briton Raducanu, the first qualifier to win the tournament four years ago, made the second round for the first time since hoisting the trophy as she defeated Japanese qualifier Ena Shibahara 6-1 6-2.

"I did feel different coming into it this year," said Raducanu, who lost in the first round in 2022 and 2024.

"I felt like I was doing the right things day to day, but still, it's in the back of your head. So I'm just very pleased to have overcome that."

Canada's Leylah Fernandez, who lost to Raducanu in the final four years ago, defeated compatriot Rebecca Marino 6-2 6-1 while 2023 Wimbledon champion Marketa Vondrousova saw off Oksana Selekhmeteva 6-3 7-6(3).

Former French Open winner Jelena Ostapenko made smooth progress with a 6-4 6-3 win over Chinese qualifier Wang Xiyu.

There were a handful of surprises, as qualifier Janice Tjen earned Indonesia's first win in a Grand Slam main draw in 22 years when she knocked out 24th seed Veronika Kudermetova 6-4 4-6 6-4.

Alexandra Eala of the Philippines got the crowd on their feet as she battled back from 1-5 in the deciding set to defeat Denmark's 14th seed Clara Tauson 6-3 2-6 7-6(11) in a nerve-searing affair at the Grandstand.

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"It was so, so difficult," said Eala. "This match is one for the books for me."