Naomi Osaka said that she had just two hours of sleep before crushing title-holder Caroline Wozniacki to sweep into the China Open final on Saturday.

The 21-year-old who represents Japan will play world number one Ashleigh Barty of Australia in Sunday's championship match, and will hope to have had a bit more rest.

The Australian Open champion said that she was so hyped up after defeating Bianca Andreescu in three thrilling sets on Friday night that she barely slept.

"I went to sleep at 4:00 a.m., I woke up at 6:00 a.m., so solid two hours, I can't really sleep after my matches," said Osaka.

"I just feel like my adrenaline's up more during the tougher matches so it makes it harder to sleep."

"It's definitely been a bit crazy time-wise," she added, having returned to the court to face Wozniacki less than 24 hours after defeating Andreescu.

But if the two-time Grand Slam champion was exhausted, it did not show in a 6-4, 6-2 victory in 84 minutes against the Dane.

Osaka held off all seven break points she faced against Wozniacki.

The world number four showed flashes of irritation as she let Wozniacki off the hook at 3-3 in the first set, tossing her racket on the floor.

But in the ninth game, the pressure on the 19th-ranked Wozniacki told, Osaka grabbing the break of service with an arrowing forehand.

Osaka, like Wozniacki a former number one, broke her opponent at the start of the second set to underline her superiority, before racing to a thumping win. However, she insisted that she was the underdog against Barty.

They have played each other three times before with the 23-year-old Australian winning twice.

Barty said that she has "never been happier" on and off the court after she saved match point against Kiki Bertens of the Netherlands in their semi-final.

The French Open champion committed 52 unforced errors but still just about emerged victorious in a nail-biting 6-3, 3-6, 7-6 (9/7) triumph.

Barty, who surged to the top of the rankings in June, said there had been "massive growth" in her mental fortitude when she faces crunch points.

"That's gone hand-in-hand with adding some new people to my team, trying to work with them behind the scenes," Barty, who five years ago took a break from tennis and played cricket, said.

"Not just for my tennis – it's for my life, my health and well being, as well, which has been the best thing. I have never been happier off the court, never been happier on the court."

Top seed Dominic Thiem fought back from a set down to reach the China Open finals in the men's draw -- and also book his place at the season-ending ATP Finals, having beaten Russia's Karen Khachanov 2-6, 7-6 (7/5), 7-5 in two hours and 41 minutes.

The Austrian will play 21-year-old Stefanos Tsitsipas of Greece who triumphed 7-6 (8/6), 6-4 in a battle of the rising stars against 22-year-old Alexander Zverev of Germany.

Thiem, who has now reached the ATP Finals for a fourth time in a row, said, "For me personally, it was one big goal when I started into the season, I'm very, very happy that I made it (the London Finals) again.

"But it's not because of today's win, it's because of all the season."

(With input from AFP)