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
Fourth seed Holger Rune suffered a shock defeat in the US Open first round as former champion Dominic Thiem claimed an emotional win.
Rune lost 6-3 4-6 6-3 6-2 to world number 63 Roberto Carballes Baena of Spain on court five.
The 20-year-old Dane had made a pointed comment about his court assignment before the match.
Earlier, Thiem beat 25th seed Alexander Bublik to claim his first Grand Slam match win in more than two years.
There were also wins for last year's runner-up Casper Ruud, ninth seed Taylor Fritz and 2022 semi-finalist Frances Tiafoe on the first day's play in New York.
Serbia's Novak Djokovic, seeded second behind Spain's Carlos Alcaraz, did not start his opening match against France's Alexandre Muller until 23:00 local time [04:00 BST].
'High intensity' Rune suffers early exit
Denmark's Rune reached the Wimbledon quarter-finals in July but has played only twice since, with both matches ending in defeat.
The lack of form coming into the last major of the season clearly played a role, with Rune also taking a medical timeout for treatment on his left leg.
Speaking on BBC Radio 5 Live, Great Britain's Davis Cup captain Leon Smith said Rune had looked "irritable" during practice sessions.
"There were signs that something was not quite right. He was hitting tennis balls way up into the stand," said Smith.
"Rune plays really high intensity - really engaged with the crowd, constantly getting hyped up, and that is tiring.
"The way he plays he needs to be on it mentally and emotionally."
Speaking after the loss, Rune said he "did not expect" to play on the smaller court five instead of one of the main show courts.
"I feel like it's normal. I mean, the better you get in the rankings, it's more, benefits you should get with playing in better conditions," he said.
"So I think that's a normal way and it's also how the ATP do it with all the players.
"But they didn't do it with me here. That's obviously disappointing, but not going to blame the court on the loss."
Today is pretty special - Thiem
Thiem's last win at a Grand Slam came at the 2021 Australian Open, where he reached the fourth round.
The 29-year-old had lost in the first round in his past six Grand Slam appearances.
However, it was fitting that he found his form in New York, the city where he fought back to beat Alexander Zverev and claim a long-awaited major title in 2020.
The Austrian put in a solid display to beat 25th seed Bublik 6-3 6-2 6-4.
"Today is pretty special. It means a lot to me that this first Grand Slam victory after this injury happened here at the US Open. I couldn't have wished for a better place like here with all the memories," Thiem added.
"It was my first major injury on my wrist, which is very important for my game. It just took time to recover and to get the confidence back in the wrist."
Thiem had faced a tricky opponent in Bublik, who marked his best run at a Grand Slam with a fourth-round showing at Wimbledon, but the Kazakh struggled for consistency.
He hit 17 double faults in an error-strewn performance, with Thiem serving out the match at the second attempt to set up a meeting with rising American star Ben Shelton.
"The Grand Slam victory in 2020 unfortunately came without the crowd [due to Covid-19 protocols] so I'm super happy that all the fans are back," he said.
"I hope I can make another good run with all the energy from the crowd."
What else happened on day one?
Fifth seed Ruud, runner-up to Djokovic at the French Open earlier this year, beat American qualifier Emilio Nava 7-6 (7-5) 3-6 6-4 7-6 (7-5) on Court 17.
Ninth seed Fritz has struggled at Grand Slams, making it past the third round on just two occasions in his career, but overcame compatriot Steve Johnson 6-2 6-1 6-2.
On Arthur Ashe Stadium, 10th seed Tiafoe, who produced a memorable run to the semi-finals last year, beat fellow American Learner Tien 6-2 7-5 6-1.
Alejandro Davidovich Fokina also came through easily, beating American Marcos Giron 6-4 6-4 6-2.
Later on Monday, Djokovic plays his first US Open match since 2021 as he kicks off his campaign on Arthur Ashe Stadium against world number 84 Alexandre Muller.
Seventh seed Stefanos Tsitsipas takes on former Wimbledon finalist Milos Raonic, who is making his comeback after nearly two years out due to injury, in the night session.