Naomi Osaka is the reigning US Open champion, the first Japanese to win a Grand Slam singles title and a fast-rising star of tennis – but do not call her cool.

Osaka bolstered her growing fame as she thrashed unseeded American Danielle Collins 6-1, 6-0 in 53 minutes to saunter into round three of the China Open on Tuesday.

Told afterwards that she had been branded “Queen of Cool” by an Australian tennis magazine, the 20-year-old looked startled.

“I don’t like the word ‘cool’ because then I feel like when someone meets me, they’ll be disappointed or something,” Osaka told reporters in Beijing.

“So they can use ‘expressionless’ or something,” she added with a smile, playing with the impression formed by some observers.

“I think actually I’m very emotional.”

Osaka, whose maiden Grand Slam was overshadowed by Serena Williams’s row with the chair umpire in their New York final, faces 10th seed Julia Goerges next at the China Open.

Osaka has booked her spot in the season-ending WTA Finals Singapore for the first time, underlining her blossoming potential.

But the world number six has appeared to struggle mentally with the fallout from the tempestuous final at the US Open, where Williams branded Carlos Ramos “a thief” and later accused him of sexism.

Osaka says her breakthrough victory last month was “bittersweet”, but has refused to point the finger at the American great.

“For me, I don’t know, I don’t know, the memory of the US Open is a little bit bittersweet,” Osaka said.

“Right after, the day after, I really didn’t want to think about it because it wasn’t necessarily the happiest memory for me.

“I just sort of wanted to move on at that point.”

The young Japanese light-heartedly compared her Grand Slam success to green-tea ice cream.

“When you bite into it, it’s sweet, but also very strong – that’s how that memory feels to me.

“Of course I’m happy that I won a Grand Slam, I don’t think there’s anything that can take away from that... but I feel like it was so strange, I didn’t just want to think about it.”

With AFP inputs