US Open title 'not the happiest memory': Osaka

Naomi Osaka made the startling admission on Monday that winning the US Open was "bittersweet" and "not the happiest memory" and revealed that she has been trying to forget about the career-defining victory.

The 20-year-old rising star from Japan stunned Serena Williams last month in a tempestuous final in which the American called chair umpire Carlos Ramos "a thief" and later accused him of sexism.

"There's a lot of stuff I want to say about how I felt and whatever," the world number six said.

Williams's high-profile meltdown made headlines over Osaka's feat in becoming the first Japanese to win a Grand Slam, although Osaka has declined 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."

Speaking in Beijing, where Osaka powered into round two of the China Open with a dominant performance over Kazakh qualifier Zarina Diyas, 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.

"I wanted to just push it to the side."

Osaka, who defeated Diyas 6-4, 6-3 despite not playing her best, faces unseeded American Danielle Collins next.

Also safely through on Beijing's outdoor hard courts is another reigning Grand Slam champion, Australian Open winner Caroline Wozniacki.

With world number one Simona Halep retiring from the tournament with a back injury and Serena Williams absent, Osaka and Wozniacki are among the favourites.

Former world number one Wozniacki was emphatic with a 6-2, 6-3 demolition of Switzerland's Belinda Bencic.

Wozniacki will play Croatia's unseeded Petra Martic in round two.

It was a case of seventh time lucky for another former number one, Garbine Muguruza, as the Spaniard set up a meeting with Aryna Sabalenka of Belarus.

Muguruza, who is down to 15th in the world, made a fast start as she hammered Ekaterina Makarova 6-0, 6-4, making the seventh match point count against the Russian.

Elise Mertens, the 15th seed from Belgium, suffered a surprise defeat to home player Zhang Shuai, the Chinese winning 6-1, 3-6, 6-3.

Also out is the 17th seed Madison Keys after the American, the 2017 US Open finalist, withdrew with a knee injury.

The top men's seeds make their entrance on Tuesday, with Juan Martin del Potro, Alexander Zverev and Grigor Dimitrov all in action.