Four-time Grand Slam champion Naomi Osaka lost in the first round of a second consecutive major tournament.

Danielle Collins, an American seeded 19th, beat Osaka 7-6 (5), 6-3 in a big-hitting matchup at the US Open.

Collins reached her first Grand Slam final at the Australian Open in January and showed that same sort of hard-court form in her victory over former No 1 Osaka.

Entering this contest, Osaka held a 3-0 career edge against Collins, winning every set they had played.

Osaka won the US Open in 2018 and 2020, and the Australian Open in 2019 and 2021. This season, she lost in the third round in Australia, the first round at the French Open, then sat out Wimbledon.

Osaka is now ranked 44th, which means she could have been drawn to face anyone in the first round.

Earlier, Emma Raducanu became only the third defending US Open champion to lose in the first round, eliminated by Alizé Cornet 6-3, 6-3.

Raducanu, who was 18 and ranked 150th when she won the title as a qualifier a year ago, was bothered by hand blisters — she took a medical timeout for treatment after the first set — and was outplayed by Cornet, a 32-year-old from France who also upset No 1 Iga Swiatek at Wimbledon.

"Obviously really disappointing. Really sad to leave here. It's probably my favorite tournament. But also, I mean, in a way, [I'm] happy, because it's a clean slate," Raducanu said.

"I'm going to drop down the rankings. [Will] climb my way back up."

Also playing under the lights was 22-time major champion Rafael Nadal, who returned to the US Open for the first time since 2019 and beat Australian 21-year-old Rinky Hijikata 4-6, 6-2, 6-3, 6-3.

Despite the early first set stumble, Nadal did not show any serious lingering issues with the torn abdominal muscle that forced him out of Wimbledon in July.

Nadal's victory was followed at Arthur Ashe Stadium by a match between four-time Grand Slam title winner Naomi Osaka and 2022 Australian Open runner-up Danielle Collins.

In other action on a humid and windy Day 2 at the hard-court tournament, women's winners included 2017 champion Sloane Stephens, No 1 Iga Swiatek, No 6 Aryna Sabalenka, No 8 Jessica Pegula, No 9 Garbiñe Muguruza, No 13 Belinda Bencic — whose opponent, Andrea Petkovic, said she is retiring from pro tennis — and No 22 Karolina Pliskova, the 2016 runner-up in New York.

Men who advanced included 2014 champion Marin Cilic, No 3 Carlos Alcaraz, No 7 Cam Norrie, No 8 Hubert Hurkacz, No 9 Andrey Rublev, No 11 Jannik Sinner, No 15 Marin Cilic, No 17 Grigor Dimitrov and No 28 Holger Rune, who meets John Isner next.

Venus Williams out of US Open

The welcome and support for Venus Williams in Arthur Ashe Stadium were not the same as they were for her sister, Serena, a night earlier. Nor was the result.

Venus, who turned 42 in June, has not made any pronouncements about her future in tennis, unlike her younger sibling, and while she has been successful and influential, too — a seven-time Grand Slam champion; a black woman in a predominantly white sport — the fanfare and attention are not the same.

Playing in front of thousands of empty blue seats in an arena quite silent at the start, although growing louder later, Venus bowed out in the first round of the US Open for the second consecutive appearance, losing 6-1, 7-6 (5) to Alison Van Uytvanck.

"She means so much to female tennis. Tennis, in general," Van Uytvanck said. "She's a legend."

This was the 23rd trip to Flushing Meadows for Venus, who made it to the final in 1997 as a teen then won the trophy in 2000 and 2001, and her record 91st time participating in a major tournament.

Venus had never lost in the opening round at the US Open until 2020, then was absent last year.

Asked what keeps her motivated these days, she answered: "Three letters: W-I-N. That's it. Very simple."

Venus was off the tour in singles entirely from August 2021 until less than a month ago and is now 0-4 since her return. Her ranking — which 20 years ago was No 1 — is 1,504th this week.

"It was definitely the longest time I have been away from tennis and been without a racket in my hand. So it was a completely new experience for me, getting a racket back in my hand and trying to acclimate as quick as possible to be ready for the US Open, which was not easy," she said.

"Definitely playing lots of great points, but in the end, it's just rust. There is nothing you can do about that except for, you know, not be rusty at some point."

It was Serena who announced to the world on August 9 that she was getting ready to step away from her playing career, leaving unclear exactly when the end would be, although she hinted it could come at the US Open.

So her first-round match Tuesday fell into the category of a must-see happening, drawing a record crowd of more than 29,000 to the tournament grounds, including more than 23,000 in Ashe — and the atmosphere was uproarious and electric from start to finish of her 6-3, 6-3 victory over Danka Kovinic.

Now Serena, who won six of her 23 Grand Slam singles titles in New York, will move on to a matchup against No 2 seed Anett Kontaveit in Ashe on Thursday.

And then she and Venus will join forces in doubles on Friday, teaming up for the first time anywhere since 2018 this week.

When a reporter wanted to know whether retirement has been on Venus' mind, she replied: "Right now, I'm just focused on the doubles."

So how did that reunion of a pairing that has earned 14 Grand Slam titles in that event come about?

"It was Serena's idea. She's the boss, so I do whatever she tells me to do," Venus said. "We have had some great wins. It would be nice to add some more."

Van Uytvanck now meets Clara Burel, who eliminated Wimbledon champion Elena Rybakina 6-4, 6-4.