NEW YORK, Aug 30, 2024 (BSS/AFP) - Naomi Osaka's return to the US Open ended in the second round on Thursday, but the two time champion said she felt "grateful" as she departed in the wake of a straight-sets loss to Karolina Muchova.

"It was really fun," Osaka said after falling 6-3, 7-6 (7/5) to the 52nd-ranked Czech under the lights on Arthur Ashe Stadium. "I felt very grateful that there were so many people cheering. I missed it a lot."

Japan's Osaka won the title in 2018 and 2020 but missed last year's edition after the birth of her daughter Shai.

She has been unable to build momentum in her comeback, and her first round win over Jelena Ostapenko was her first in four years over a top-10 player.

"I think this year for me has been a learning year," she said. "I put a lot of energy and effort into all the tournaments that I played.

"Australian Open was so fast, so I probably forgot that one. I enjoyed learning how to enjoy the French Open. I haven't been to Wimbledon in years, so it was nice to go back there."

But Osaka hasn't reached the third round of a Grand Slam since the 2022 Australian Open and she acknowledged that she was combatting a dip in form even before her maternity break.

"I feel like I'm coming back from pregnancy, but also it wasn't like in 2022 I was the best version of myself," she said. "So in some way I had to catch up to that, and then also I'm trying to pass it at the same time.

"It's been a little difficult because obviously I can only gauge how I'm doing by results. I feel faster. I feel better, but I lost in the second round. So it's a little rough."

Osaka returned to Ashe -- where she captured her first Grand Slam title with an upset of Serena Williams in 2018 -- in style, stepping on court in a made-for-the-lights black version of her ruffled and ribboned custom Nike US Open kit, her hair studded with pearls.

She made a confident start, but she couldn't convert an early break point and there were too many miscues in the face of devastating pressure from Muchova at the net.

The Czech broke for a 4-3 lead in the first as she put together a run of five straight games.

Osaka stopped the rot with a steely hold for 1-1 in the second set and broke Muchova for a 5-4 lead in the second.

But she wasted three set points in the next game as Muchova regained the break, leveling the set when Osaka smashed a forehand long.

Osaka had a 4-2 lead in the tiebreaker when her fourth double fault opened the door. Muchova won four straight points to give herself a pair of match points, Osaka saving one before she banged another wild forehand long.

- 'Atmosphere and energy' -

It was a satisfying win for Muchova, who is on the comeback trail herself.

A semi-finalist at New York last year, she reached a high of eighth in the world before she missed nine months after undergoing wrist surgery.

"It's a long journey," she said. "It's a year. I'm for sure in a different position than I was last year. I don't even want to compare myself to last year -- it was kind of a bumpy road.

"I had the surgery, and I didn't know if I will play or not. I'm just really grateful honestly that I'm here, that I can play, that I'm pain-free, and that I have a chance to play these matches.

"The court and the atmosphere is amazing," Muchova added. "They were mostly cheering for Naomi, but that's natural. But I just think so many people coming out and the show and everything about that -- I would say it's why I play tennis and what I like about it, the atmosphere and the energy."