Iga Swiatek began her bid to capture a second US Open title with an uneven straight-sets win over lucky loser Kamilla Rakhimova on Tuesday as Jannik Sinner and Carlos Alcaraz take their first steps towards a potential semi-final blockbuster.
World number one and 2022 champion Swiatek saw off 104th-ranked Rakhimova of Russia 6-4, 7-6 (8/6) to extend her season-leading record to 54 match wins.
However, it was an unconvincing display by the Pole who committed 41 unforced errors and had to fight off three set points in the second set before she steadied the ship.
"I try to adapt to the court and feel how it is," said French Open champion Swiatek after her win on Arthur Ashe Stadium.
"I'll take it day by day to get more rhythm. It's the biggest stadium we have and you feel it's a huge deal."
World number one Sinner plays his first match since it emerged he had twice tested positive for a banned substance but had escaped a lengthy ban.
The 23-year-old was cleared of any wrongdoing over the presence of anabolic agent clostebol after it was ruled he had been inadvertently contaminated by his physio, who had used a spray to treat a cut to his own hand.
"In my mind I know that I haven't done anything wrong," said Australian Open champion Sinner who faces 140th-ranked Mackenzie McDonald.
Sinner has endured a rollercoaster relationship with the US Open.
Twelve months ago, he was defeated in five sets by Alexander Zverev in the last 16 while in 2022 he was knocked out by Alcaraz in a five-set quarter-final which finished just before 3 a.m.
Third seed Alcaraz won the first of his four Grand Slam titles in New York in 2022 before going on to become the youngest world number one.
The 21-year-old opens the night session on Arthur Ashe Stadium against Australian qualifier Li Tu, the world number 186.
Alcaraz is on a 14-match winning streak in Grand Slam events and is attempting to become the only third man in the modern era to win the French Open, Wimbledon and US Open in the same year after Rod Laver in 1969 and compatriot Rafael Nadal in 2010.
Li, 28, hasn't won a match on the main tour in 2024.
However, his clash against Alcaraz will be emotional as the tournament falls on the second anniversary of the death from cancer of his mother, Yu Ping Zheng.
In early action, 2021 semi-finalist Felix Auger-Aliassime, the 19th seed, slipped to a straight-sets loss to Jakub Mensik of the Czech Republic.
Danielle Collins of the United States, who is playing her last season on tour, was knocked out in three sets by compatriot Caroline Dolehide.
Two-time US Open champion Naomi Osaka, who missed last year's US Open after giving birth to her daughter Shai, faces 2017 French Open champion Jelena Ostapenko.
"She's honestly one of my favourite players to watch. I think we are polar opposites in a way," said former world number one Osaka now ranked at 88.
Ostapenko made the quarter-finals in New York last year, defeating Swiatek on the way.
Osaka, who appeared on court wearing a giant bow on the back of her jacket as well as a frilly, detachable skirt, is not the only former US Open champion in action on Tuesday.
Stan Wawrinka, the 2016 winner, aims to become the third man in last 50 years to win a main draw match at the tournament at the age of 39 or over after a 40-year-old Jimmy Connors in 1992 and Ken Rosewall -- who was 42 when he achieved the feat in 1977.
Britain's Emma Raducanu, the 2021 champion, begins against 2020 Australian Open winner Sofia Kenin.
Canada's Bianca Andreescu, the New York champion in 2019, takes on French Open and Wimbledon runner-up Jasmine Paolini.
Daniil Medvedev, the Russian fifth seed who shattered Novak Djokovic's dream of a rare calendar Grand Slam by claiming the 2021 US Open, meets Dujan Lajovic of Serbia.
Former Australian Open champion Caroline Wozniacki faces Japan's Nao Hibino.
Fourth seed Elena Rybakina, the 2023 Wimbledon champion, meets 194th-ranked Australian qualifier Destanee Aiava.
