The Japanese star powered past third seed Gauff 6-3, 6-2 in a highly-anticipated but lopsided fourth-round showdown of former US Open champions on the Labor Day holiday in New York.

Osaka broke in the very first game in front of an expectant Arthur Ashe Stadium crowd and was untouchable on serve in a ruthless display against a misfiring Gauff, who hit 33 unforced errors.

"This is my favourite court in the world and it means so much to me to be back today," said Osaka, who looks primed for a tilt at a fifth Grand Slam.

"This is kind of uncharted territory at this point of my career," added Osaka. "I'm just enjoying it. I'm having fun."

The 27-year-old, a two-time US Open champion, is enjoying her deepest run at a major since winning her second Australian Open title in 2021.

It has been a painstaking climb back towards the top of the game for Osaka, who returned to tennis last year following the birth of her daughter in 2023.

"I was in the stands two months after I gave birth watching Coco and I just really wanted an opportunity to come out here and play," said Osaka, who also beat a 15-year-old Gauff at the US Open in their first meeting in 2019.

Gauff conceded the mental toll of a challenging first week and the efforts to remodel her faltering serve had weighed heavily on her.

"I think emotionally how much this week was, I think today I just stepped in, and I maybe was a little bit empty," she said.

Osaka plays Czech 11th seed Karolina Muchova in Wednesday's quarter-finals. Muchova beat Ukrainian 27th seed Marta Kostyuk 6-3, 6-7 (0/7), 6-3 and is seeking a third straight semi-final at Flushing Meadows.

- Swiatek 'in the zone' -

Swiatek brushed off Russian 13th seed Ekaterina Alexandrova 6-3, 6-1 in barely an hour to extend her Grand Slam winning streak to 11 matches as she targets a second US Open crown.

"I felt like in the beginning she played fast but later on I felt in my bubble, in the zone," said Swiatek.

The Polish second seed faces Amanda Anisimova in a repeat of the Wimbledon final, which Swiatek won 6-0, 6-0. The American thumped Brazilian 18th seed Beatriz Haddad 6-0, 6-3.