Naomi Osaka's wait for a deep run into a grand slam rolls on after the former world number one was beaten by Karolina Muchova at the US Open.

Osaka, a two-time champion at Flushing Meadows, lost 6-3 7-6 (7-5) on Thursday.

She came up against a player in fine form in Muchova, with the Czech displaying the quality that saw her reach the semi-finals a year ago.

"I was just really trying to be focused," Muchova said.

"I know she's an amazing player and that I have to bring the A-game to have a chance. So I was just trying to be really focused on myself. I knew I had to serve well because her serve is really good. So I was just trying to be kind of locked in myself and focused out there."

"Then the energy and the big court and all that, it for sure helps me. I like that."

Osaka, meanwhile, suggested the nerves got to her on Arthur Ashe Stadium.

"I think during the pressure moments I got nervous," Osaka said, and I don't know if I just have to keep playing more matches and get used to that feeling, especially on a really big stage.

"Honestly, if I get past the disappointment, I feel pretty proud of myself to have gotten that many opportunities while still feeling like I could have played much better."

Data Debrief: Fifth time's the charm?

Muchova is one of nine players to have defeated five former world number ones at grand slam events.

However, out of those, she is the only active player yet to win a major or a WTA 1000 title. Will that change in New York?