Two-time champion Naomi Osaka said it feels like “my heart dies every time I lose” after her US Open comeback ended in a second-round defeat by Karolina Muchova.

Japan’s Osaka, who won the title in 2018 and 2020, missed last year’s tournament after giving birth to her daughter Shai.

The 26-year-old claimed her first top-10 victory in over four years when she beat Jelena Ostapenko in the first round.

However, she could not topple Czech Muchova, losing 6-3 7-6 (7-5) after squandering three set points to force a decider.

“It’s a little rough because I do take these losses really personally. It’s like a dramatic word, but I feel like my heart dies every time I lose,” she said.

“I’ve been trying to be more mature and learn and talk more about them.”

Osaka, who also won the Australian Open in 2019 and 2021, spoke before the US Open about not feeling “like I’m in my body” since her return from maternity leave.

She returned to the WTA Tour in January, but has not gone beyond the quarter-finals of any event – losing in the second round of Wimbledon and in the French Open this year, while she fell at the first hurdle at the Australian Open.

Despite the early exits, the four-time major winner said 2024 had been a “learning year”.

“It’s been a little difficult because obviously I can only gauge how I’m doing by results. Like, I feel faster. I feel better, but I lost in the second round. So it’s a little rough,” the former world number one said.

“But, also, it’s been fun playing a lot of tournaments. It’s been a commitment for sure, but I’ve been able to go to different cities that I’ve never been to.”

Having lost the first set, Osaka – to the delight of the New York crowd – was just one point away from taking Muchova to a third set.

But she missed all three set-point opportunities and threw her racquet down in disgust as her opponent levelled at 5-5.

In the tie-break, Osaka let a two-point advantage slip and gifted Muchova the victory when she slammed a simple forehand wide.

The 2023 French Open runner-up described her win over Osaka as “the cherry on top”.

Muchova reached the semi-finals at Flushing Meadows last year before suffering a wrist injury that would require surgery and keep her sidelined for 10 months.

“This year, the biggest win for me is that I could play again. I’m really grateful I am able to play tennis and I made it here,” Muchova said.

She will face Anastasia Potapova in the third round after the Russian defeated American Varvara Lepchenko.