The German sixth seed was overpowered by the impressive 19-year-old.

Osaka, ranked 45th in the world, eased through the first set 6-3 before taking the second 6-1 in the Arthur Ashe Stadium at Flushing Meadows.

It made amends for her loss from 5-1 up against American Madison Keys in the third round of last year's event.

 "It means a lot, especially since last time I was here," Osaka said.

"This court has not given me fond memories but hopefully this overtakes that.

"When it was 4-1 today I was thinking, 'I really hope I don't do what I did last year' and that let me focus a lot."

Kerber has endured a disappointing year since her victory last year, having not won a title since.

Men's world number one Rafael Nadal has enjoyed a superb 12 months, conversely, and he continued that run with a 7-6 (8-6), 6-2, 6-2 win over Serbia's Dusan Lajovic elsewhere today.

It came on a rain disrupted day in which all matches on the roofless outside courts were cancelled.

Roger Federer was another winner.

The Swiss champion was made to dig deep, though, before beating American Frances Tiafoe 4-6, 6-2, 6-1, 1-6, 6-4.

Women's top seed Karolina Pliskova also managed to start well in her bid for a first Grand Slam title.

The Czech world number one eased past Poland's Magda Linette 6-2, 6-1.

She will be hoping to go one better than her runners-up finish last year.