Former Australian Open champion Naomi Osaka fought back from a set down Wednesday to reach the third round of a Grand Slam for the first time since the birth of her daughter in 2023, gaining a "little revenge" for defeat at the U.S. Open.

The Japanese star, who won in Melbourne in 2019 and 2021, dropped the first set against 20th seed Karolina Muchova before winning 1-6, 6-1, 6-3.

It was her second three-set examination in two days after being pushed all the way by Caroline Garcia in the first round.

"Honestly, it took everything," Osaka said when asked how she turned the match around. "I felt like I left everything I had on the court. I could have done better, but just to be back on these courts... It really makes my whole year."

The Czech Republic's Muchova was victorious when the pair last met, at the 2024 U.S. Open, and she was out of the blocks quickest, sweeping to the first set in 32 minutes.

Osaka hit back with a double-break before closing out the second set with a rapid service game.

Osaka continued to improve against a dangerous opponent who made the semifinal in Melbourne four years ago.

The former world number one Osaka, on the back of some blistering groundstrokes, struck the first blow in the decider as she broke for a 3-2 lead.

A searing backhand winner down the line saved a break point in the next game and another consolidated her advantage at 4-2.

A second break sealed the match in 1hr 57min to set up a third-round clash with Belinda Bencic of Switzerland for a place in the last 16.

"It means a lot, she's an incredibly difficult opponent for me to play," said Osaka of Muchova.

"She crushed me in the U.S. Open when I had my best outfit ever," she laughed. "I was so disappointed. I was so mad. This was my little revenge."

In early men's action, four-time Grand Slam winner Carlos Alcaraz said he was "really, really happy" with his form after an ominous display of strengthto sprint into the third round.

The Spanish third seed showed no mercy to Japan's Yoshihito Nishioka, who was taught a 6-0, 6-1, 6-4 lesson on Margaret Court Arena in an 81-minute rout.

"I think I played really solid today," said Alcaraz, who won Roland Garros and Wimbledon last year but is yet to go beyond the quarterfinals at Melbourne Park. "I improved the things that I had to improve from the first match. Just really, really happy with everything today. An important win for me. Three straight sets with a really high level. Hopefully continue like this."

Alcaraz tweaked his serve in the off-season and is in Melbourne with a lighter racquet, with the dividends evident.

He fired down 14 aces and won 89 percent of his first-serve points.

"I'm really happy with the serve today. It's something I worked on in the pre-season," he said. "In the first round I struggled a bit. But I spent more time yesterday practising my serve, it's something I really want to be better. I'm really glad that today it worked pretty well and hopefully in the next round it's going to be better."

Alcaraz is bidding to become the youngest men's winner in Australia since Novak Djokovic won the first of his 10 titles in 2008.

Should he do so, he will also be the youngest man to complete a career Grand Slam, with his sizzling form so far boding well for the 21-year-old.

He eased through his first-round match in straight sets and came out firing against the 65th-ranked Nishioka.

The Japanese player could barely get his racket on the ball in the first set, winning just two from 16 points at the baseline and only four points in the entire set.

Alcaraz pounded down five aces in the second set and won a formidable 91 percent on first serve to give Nishioka no chance.

The Japanese player did his best to make a match of it in the third set, but the gulf in class was too wide with the win a formality.

"The less time you spend on court in the Grand Slams, especially in the beginning, it is going to be better," added Alcaraz. "Physically I'm feeling great and I was just focused with spending as little time as I can on court."

He will next play Portugal's Nuno Borges, who beat Australia's Jordan Thompson 6-3, 6-2, 6-4.