US Open 2023
Venue: Flushing Meadows, New York Dates: 28 August-10 September
Coverage: Daily live text and radio commentaries across the BBC Sport website, app, BBC Radio 5 Live and 5 Sports Extra
American hope Coco Gauff survived a scare as she fought back to beat German qualifier Laura Siegemund in the US Open first round.
Gauff, 19, was outplayed in the first set but turned things around to win 3-6 6-2 6-4 in the New York night session.
Earlier, Polish top seed Iga Swiatek began her title defence with a 6-0 6-1 win over Sweden's Rebecca Peterson in just 58 minutes.
Greek eighth seed Maria Sakkari was the biggest casualty on day one.
Sakkari, 28, has now lost in the first round of the past three majors after she was beaten 6-4 6-4 by Spanish world number 71 Rebeka Masarova.
Elsewhere, fourth seed Elena Rybakina - who had struggled in the build-up with a shoulder injury - beat Ukraine's Marta Kostyuk 6-2 6-1, while Brazilian 19th seed Beatriz Haddad Maia beat 2017 champion Sloane Stephens.
Danish former world number one Caroline Wozniacki, who retired in January 2020 and has since had two children, marked her return to Grand Slam action in style with a 6-3 6-2 win against Russian qualifier Tatiana Prozorova.
"It feels amazing to be back. I was nervous coming out here but to get a win under my belt feels so special," said two-time runner-up Wozniacki, who plays 11th seed Petra Kvitova next.
Gauff and Swiatek through in contrasting fashion
Sixth seed Gauff is among the favourites to challenge Swiatek at the final major of the season, having won the two biggest titles of her career - at Washington and Cincinnati - in the build-up.
But she was made to dig deep against 35-year-old Siegemund, who has fallen down the rankings amid injury struggles.
Gauff was unable to match Siegemund's intensity in a first set where the German played with variety and was particularly clinical at the net.
With a star-studded crowd including former United States president Barack Obama, his wife Michelle, 2006 champion Maria Sharapova and boxer Mike Tyson watching her, Gauff had some problem solving to do.
The teenager broke in the first game of the second set, an epic which lasted 26 minutes and saw Gauff finally convert an eighth break point.
That proved pivotal as she used the momentum to quickly level the match.
Gauff broke twice to lead 3-0 in the decider and, after losing patience with Siegemund's time-wasting, overcame a late wobble to progress.
The pair shared a terse handshake after a fiery third set where both argued with umpire Marijana Veljovic about the time Siegemund was taking between points.
Asked on court to describe the match, Gauff, who will face 16-year-old Russian Mirra Andreeva in the second round, responded: "Slow. It was a tough match, I wasn't playing my best tennis.
"Laura is not an easy opponent and fights until the end. I overcame a lot of adversity so I was happy to get through."
In contrast, Swiatek made quick progress against world number 86 Peterson.
The world number one, who could lose the ranking to Aryna Sabalenka at this tournament, earned her 16th consecutive straight-set victory in the first round of a Grand Slam.
"I was happy to play a great game, with all the pressure and expectations, I was happy on the court," said four-time major champion Swiatek, who faces Australia's Daria Saville next.
"I remember when I played my first matches [at the] US Open, I always felt like there is so much going on around, and it was a little bit tougher to focus. But this year I didn't feel it."
Sakkari shocked and Rybakina through
Two-time major semi-finalist Sakkari became the first top-10 player to fall in the women's draw.
Sakkari raced to a 4-1 lead in the first set but ended up suffering a shock defeat, leaving her in tears during her post-match news conference.
"If I played five or 10% better I would have won this match. These are the matches I have to win, these are the matches I cannot lose," she said.
"There have been too many for my level this year. It is unfortunate. I thought I would turn it around here but I was wrong. I have not much to say, I'm sorry."
Stephens, who was the last American to win the singles title, was beaten 6-2 5-7 6-4 by Haddad Maia with five breaks traded in a thrilling deciding set.
Victoria Azarenka, a three-time finalist who is seeded 18th, made light work of France's Fiona Ferro in a 6-1 6-2 win.
Czech 10th seed Karolina Muchova clinched a 6-4 6-0 win over Australia's Storm Sanders, while Kvitova won 6-1 7-6 (7-5) against Spain's Cristina Bucsa.
Swiss 15th seed Belinda Bencic cruised past Kamilla Rakhimova 6-2 6-4 and plays British qualifier Lily Miyazaki next.
Former Australian Open finalist Jennifer Brady won a match at a Grand Slam for the first time since 2021.
The American has struggled with injuries over the past two years but claimed a 6-3 7-6 (7-4) win over Australian Kimberly Birrell.
'Swiatek not the same, so could be Coco's year' - analysis
Former British number one Annabel Croft on BBC Radio 5 Live
Iga Swiatek is not quite as dominant as she was last year.
She's lost to quite a lot of her nearest and dearest rivals - including Gauff. I think Gauff is looking as if she's ready to go on and win her first Grand Slam title.
Whether or not she can deal with that emotionally with it being her home Slam, and all the pressure that brings with it, I'm not sure.
It feels very wide open. Can Ons Jabeur rebound after that emotional breakdown at Wimbledon, which was so painful to watch?
There's many names you could look at like Aryna Sabalenka, who also hasn't looked quite her best recently, and Rybakina. We've also got Karolina Muchova, who reached the finals of the French Open.
Can he ever give up looking for his missing son? James Nesbitt stars in a tense drama about the aftermath of a child's disappearance
Behind the scenes in London's most expensive hotel: It costs up to £27k a night and no request is too big...