Japan's Naomi Osaka dismissed Jennifer Brady in straight sets to win the Australian Open in dominant style for her fourth Grand Slam title on Saturday.

Osaka edged a tight first set but controlled the second to win 6-4, 6-3 in 77 minutes in front of thousands of fans at Rod Laver Arena.

Third seed Osaka preserves her 100 percent record in Grand Slam finals after winning the 2018 and 2020 US Opens and the 2019 title in Melbourne. 

"We played in the semis of the US Open a couple of months ago and I told everyone that you're going to be a problem," Osaka told Brady at the trophy presentation.

"And I was right. It's really incredible to me to see your growth over the past few months, it's really cool for me to see."

The 23-year-old, who becomes only the third player after Monica Seles and Roger Federer to win their first four major finals, will now rise to second in the world rankings. 

Osaka, rated as the world's top-earning female athlete, saved two match points in the fourth round against Garbine Muguruza before going on to lift the trophy.

Osaka wore down fellow big-hitter Brady with consistency, and lifted her racquet above her face in a muted celebration of her win as the crowd roared.

The sweeping win confirms Osaka's status as tennis's leading light having brushed aside Williams in straight sets in the semi-finals. 

She has won half the majors she's contested since beating Williams to win her first Slam title.  

Epic semifinal

Osaka has now claimed back-to-back Slams twice and she survived a seesaw start to gain control, reeling off six straight games en route to the title.

It was a rematch of last year's epic US Open semi-final, dubbed by some as the best match of 2020, but Osaka triumphed far more comfortably on this occasion. 

She showed no nerves at the start, firing down two aces en route to a love hold in the opening game. 

Before the match, Osaka had pinpointed her return as the key, but she was helped out by a shaky Brady who lost her serve in the fourth game after two double faults.  

But Brady, the 22nd seed, hit back with a break and she continued to pile pressure on Osaka's serve. 

A brilliant lob winner, showcasing her trademark athleticism, gave a pumped-up Brady a break point in the ninth game, but Osaka held on. 

Brady then played a sloppy game on serve to hand over the set to Osaka, who had a 20-0 record at Melbourne Park when winning the first set.

Osaka gained a stranglehold with an early break in the second set and fired down an ace to skip out to a 3-0 lead, followed by a roar of "C'mon!". 

Brady attempted a late rally, but a calm Osaka was not to be denied.

Brady's resilient run ended after serving 14 days' hard quarantine before the tournament, unlike other players who were allowed out of their hotel rooms to train.

Despite the defeat, Brady will rise to a career-high 13th in the WTA rankings.