Former champion Naomi Osaka reached the fourth round of the US Open for the first time in five years on Saturday with a three-set victory over Australian 15th seed Daria Kasatkina.

Osaka, who last reached the fourth round at Flushing Meadows during her run to the title in 2020, took advantage of Kasatkina's shaky serve to advance 6-0, 4-6, 6-3 on the Louis Armstrong Stadium court.

The win marks Osaka's best performance in a Grand Slam singles tournament since she returned to tennis last year following the birth of her daughter in 2023 -- and sets up a blockbuster fourth round clash with American third seed Coco Gauff.

"It's been a really long journey but I'm glad to be here now," Osaka said, as she looked ahead to playing in the second week of a Grand Slam for the first time since winning the 2021 Australian Open.

Osaka said she is relishing meeting 2023 champion Gauff, who she regards as her "little sister."

"Can somebody come to the match and cheer for me, because it's kind of tough playing an American here," Osaka joked to the crowd about her match-up with Gauff.

"I kind of see her as a little sister so it's kind of cool to be playing her again."

The 27-year-old four-time Grand Slam singles champion from Japan threatened to inflict a rout on Kasatkina after a one-sided first set in which the Australian scored just seven points and coughed up seven double faults.

But Kasatkina showed great resolve to rally back in the second set, breaking Osaka four times to win 6-4 and level the match at a set apiece.

Yet Kasatkina's suspect serve was once again her undoing in the decider, with Osaka breaking to take a crucial 3-1 lead in the fourth game.

That advantage would prove to be decisive, as Osaka held for the remainder of the set to close out victory.