MELBOURNE:Naomi Osaka ended Serena Williams' bid for a record-equalling 24th Grand Slam title with an imperious 6-3 6-4 win on Thursday, a victory that booked her spot in her second Australian Open final and left the American great in tears.

In a rematch of their tumultuous 2018 U.S. Open decider, Osaka underlined her status as the new queen of women's tennis and soaked up the cheers from the Rod Laver Arena crowd as fans returned to the Grand Slam after a five-day lockdown.

"It's just always an honour to play her and I just didn't want to go out really dud. I just wanted to try my best," Osaka said after her 75-minute match on a steamy afternoon.

"I was a little kid watching her play and just to be on the court playing against her is a dream."

Osaka, the 2019 champion, will meet Jennifer Brady, who ensured there would be at least one American in the final after battling to a 6-4 3-6 6-4 win over Karolina Muchova in the other semi on Thursday.

It will be a rematch of last year's U.S. Open semi-final, where Osaka edged Brady in three sets on the way to her third Grand Slam triumph.

Williams, however, exited in tears after an error-strewn match and with a question mark over her future.

The 39-year-old, who returned to the tour in 2018 after taking time away from the game to give birth to daughter Alexis Olympia, cut her post-match news conference short when she broke down after being asked whether it was a bad day at the office.

"I had so many opportunities, ... it was just ... I made too many mistakes there and easy mistakes," said the American. "Not like .... I was on the run or anything. They were just easy, easy mistakes.

"I don't know. I'm done," she added before getting up to leave the room.

HAND ON HEART

Williams' record bid ended with another near-miss, having reached the finals of four Grand Slams since her last major crown at the Australian Open in 2017.

She paused while exiting centre court as the crowd gave her a standing ovation. She put her hand on her heart, smiled and waved.

Williams was asked whether it was a final farewell to Melbourne Park, where she holds a record seven titles in the professional era.

"I don't know, if I ever say farewell I wouldn't tell anyone, so...." she responded.

Williams and Osaka's last Grand Slam clash was full of drama with the American losing her temper at the chair umpire on the way to defeat in the 2018 final at Flushing Meadows and fans jeering during the trophy ceremony.

Thursday's semi-final was uneventful by comparison, though Osaka put on a tremendous show after dropping serve in the opening game.

Williams took a 2-0 lead but the Japanese third seed won five straight games before closing out the set with a blazing forehand winner.

Williams began yelling at herself between points, trying to fire herself up, but Osaka was all cold-blooded assassin as she broke the American in the first game of the second set.

Osaka finally wavered with three double-faults to allow Williams to break back to 4-4 but Williams repaid the favour with a double-fault that produced three break points.

Osaka converted the first of them, swooping in to stroke an angled backhand winner.

She then served out the match to love, with an overwhelmed Williams bowing out with a netted backhand.

Williams had come to Melbourne Park seeking a 24th Grand Slam title but it was her 24th unforced error that ended her campaign.

Brady kept the U.S. flag flying, though, as she steadied in the late match to book her first Grand Slam final.

After needing five match points to break Muchova's resistance, Brady gets to continue a wild Australian adventure that began with 14 days in hard quarantine in the leadup.