NEW YORK — It was a tougher test than it needed to be, but fan-favorite Naomi Osaka is through to the third round at the US Open.

The two-time US Open champion stumbled through a messy second set before regaining her form and beating doubles specialist Katerina Siniakova of Czechia, 6-2, 5-7, 6-1, in Thursday’s opening match at Arthur Ashe Stadium.

Hyped to the crowd as “one of the most influential athletes on the planet,” by the stadium’s public address voice in the late morning here in Flushing Meadows, the 28-year-old Osaka looked poised for an easy day in the office after another high-fashion entrance.

After she paid tribute to NBA legend Allen Iverson for her first-round match on Monday night — a match she won in a pair of tie-breaks — Osaka took to the court wearing silver and white under a long white jacket and white visor.

But then her easy-breezy day hit a speed bump and she turned a comfortable 4-2 second-set lead into an ugly 5-7 collapse.

The 13th seed, eight years removed from her grand (and chaotic) win over Serena Williams here to claim her first Open title, then got her game back on track — specifically her serve — and raced out to a 3-0 lead in the final set and cruised to the finish line, 6-1.

Osaka, who spent part of her childhood not far from the grounds here at the Billie Jean King National Tennis Center, gave her team a little fist pump as she headed off to the net to shake hands.

“The match was definitely really tough and I don’t know, I just felt like I had to fight,” Osaka said in her post-match on-court interview. “I definitely had a couple opportunities in the second set and I think I was a little bit too hard on myself. So I took the bathroom break, regrouped a little, came back and just tried to have no regrets.”

On a day when the umbrellas were needed to combat the blazing sun — after several soggy, overcast days — Osaka started to feel the heat starting in the seventh game of the middle set. With a chance to consolidate her first break of the second set, Osaka lost her momentum and started to lose serve game after serve game.

Her frustration finally came out in the 11th game as she pounded her racket twice into the blue court of Ashe Stadium before losing the set a game later. She finished with 20 unforced errors in the set, after only committing four in the opening set that she finished in a tidy 30 minutes.

“I was a little bit too frantic,” Osaka said of the second set a few hours after the match. “I was thinking too much about closing. I feel like if I played point by point, I wouldn’t have made some of the decisions that I did.”

But she settled down and won more than 90% of her first-serve points in the deciding set to end any thought of a stunning upset.

“I think on my end it was more, like, mentally I wanted to play perfectly,” Osaka said. “Obviously that’s not going to happen every day. In the third set, I just tried to do what I could do, and thankfully I was able to win.”

Siniakova, 30, has never been much of a threat in singles here or at any Grand Slam. Although she was once ranked as high as No. 27 (2024) in singles, she lost in the first round here in three straight tournaments coming into the ’26 edition, and her best effort was the third round in 2018.

Doubles is a different story, though, as Siniakova is the top-ranked doubles player in the world and is an 11-time Grand Slam doubles champion. She will team up with American Taylor Townsend as the top-seeded team in the doubles draw.

Osaka, who also has two Australian Open titles on her resume, will next face Belgium’s Elise Mertens.

“Here obviously I’ve had a lot of good memories, and I hope to continue making them,” Osaka said.

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