The Japanese superstar crushed American Jennifer Brady 6-4 6-3 in 77 minutes on Saturday night to become the first woman since Monica Seles 30 years ago to win her first four grand slam finals.

All-time majors title leader Margaret Court also accomplished the feat in the early 1960s, as did Roger Federer before going on to rack up a record 20 men's grand slam singles crowns.

But, ominously for Osaka's rivals, not even legends Serena and Venus Williams, Steffi Graf, Martina Navratilova, Chris Evert or Billie-Jean King managed to win their first four major finals.

Still only 23, Osaka now holds two of the sport's four biggest trophies and could conceivably secure a non-calendar-year grand slam if she also wins the French Open in June and Wimbledon in July.

"Definitely for me, there's no reason why I shouldn't do well in those tournaments," Osaka said.

"It's a matter of being comfortable and hopefully as I play more matches on those surfaces I'll get better."

Osaka's latest success follows her 2019 Australian Open triumph and 2018 and 2020 US Open titles runs in New York.

The Williams sisters are the only other active players with more slams under their belts, confirming Osaka's status as Serena's successor as the new dominator of women's tennis.

"Definitely feels really crazy," Osaka said.

"This time around is a little bit more surreal than the last, just because I know how much effort I have to put in to winning one of these.

"This one to me is very special just because it's for me dedicated to my team.

"They're the ones that sort of see everything that I do, they're the ones that put in work with me."

Gracious in victory, the newly-crowned champion also paid a glowing tribute to Brady, who'd incredibly endured two weeks in hard quarantine on arrival to Australia last month after a passenger on her charter flight tested positive to COVID-19.

"I want to congratulate Jenny," Osaka said.

"We played in the semi of the US Open a couple months ago. I told everyone that would listen that you're gonna be a problem - and I was right."

Osaka had to save two match points in the fourth round last week against 2020 Open runner-up Garbine Muguruza.

But she's been untouchable ever since, world sport's highest-paid female athlete of 2020 not dropping another set for the tournament.

The world No.3 made a blazing start to the final, opening the match with an ace, holding serve to love and applying immediate pressure on Brady's.

Clearly nervous, having admitted to also feeling super tight during her semi-final win over Karolina Muchova, Brady double-faulted twice while dropping serve to love in the fourth game as Osaka opened up a 3-1 lead.

Osaka handed the service break straight back with a double-fault of her own, only to reel off six games in a row from 4-4 to seize command.

Despite dropping serve at 4-0 in the second set, Osaka was never really threatened and clinched the title on her first match point.

As well as Roland Garros and Wimbledon, Osaka is also eyeing Olympic glory in her homeland.

"Everyone knows I've been wanting to play the Olympics since I was a little kid," she said.

"It's really exciting it's going to be held in Tokyo and hopefully it goes through. For sure, it's my biggest goal this year.

"But I take every tournament seriously and I just want to be consistent. I think is my main goal this year."

Australian Associated Press