Naomi Osaka is keen to move on from the “bittersweet” memories of last month’s US Open triumph and she did just that with a ruthless display at the China Open on Tuesday.

The young Japanese star thrashed unseeded American Danielle Collins 6-1, 6-0 in just 53 minutes on Beijing’s outside hard courts to saunter into round three.

The 20-year-old Osaka, whose maiden Grand Slam was overshadowed by Serena Williams’s row with the chair umpire in New York, faces 10th seed Julia Goerges next in the Chinese capital.

Osaka’s reputation is growing fast and organisers on Tuesday said that she has booked her place in the season-ending WTA Finals Singapore for the first time.

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

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

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

Meanwhile, top seed Marin Cilic crashed out of the Japan Open in a shock 3-6, 6-4, 7-6 defeat to Germany’s Jan-Lennard Struff in the first round on Tuesday.

The former US Open champion looked to be in complete control after pocketing the first set with a brutal drive volley, but things quickly unravelled for the Croatian when Struff suddenly caught fire.

After Struff, ranked a whopping 50 places below Cilic at 56 in the world, had levelled the match, normal service appeared to have resumed in the deciding set.

Cilic, who reached the final of this year’s Australian Open, broke for 3-2 with a peach of a backhand that dipped viciously onto Struff’s toes, but the German struck back — not once, but twice — to force a tiebreak.

Struff smashed the breaker, snaffling it 7-1 with his ninth ace to complete the upset after two hours, 18 minutes.

He next plays Frenchman Jeremy Chardy, who edged a war of attrition with Bosnian Damir Dzumhur 4-6, 6-3, 6-3.

Earlier, three-time Grand Slam winner Stan Wawrinka beat Taylor Fritz 6-3, 6-4 while eighth seed Richard Gasquet also advanced, the Frenchman ousting another American, Denis Kudla, 7-6, 6-3.

Frances Tiafoe restored some pride for the United States by beating Germany’s Maximilian Marterer 7-5, 6-4.

Cilic’s demise will boost Kei Nishikori’s hopes of winning a third Japan Open crown after the local favourite won the tournament in 2012 and 2014.