The 23-year-old came through a tense battle between the world's top two players 6-3, 7-6 (7/4), 6-3 on Rod Laver Arena, raising his arms in the air and looking to the sky in celebration.
The victory earned the Italian world number one his third Grand Slam crown.
The former world number one responded on Saturday, posting a photo of an MRI taken of his left hamstring on the social media platform X with the caption: "Thought I'd leave this here for all the sports injury 'experts' out there."
It is Keys's first major title, having reached a second Grand Slam final eight years after her first in New York. She lost on that occasion to Sloane Stephens
Sinner's coach Darren Cahill said it was no surprise for him to see his young charge back in the final, but they were wary of the threat posed by Zverev's overarching desire to finally win a Slam.
The American battled injury and self-doubts last year and curtailed her season early, in October, to get married.
Swiatek said she made far too many mistakes against Keys on Rod Laver Arena and hoped to draw lessons from it.
The 19th seed powered through a thrilling semi-final on a final-set tiebreak against the world number two 5-7, 6-1, 7-6 (10/8) after Sabalenka had earlier swept aside Paula Badosa in straight sets.
The Italian top seed faces Ben Shelton on Friday, just two matches away from a first successful Grand Slam title defence after winning his maiden major crown in Melbourne last year.
The world number four wasted little energy to swat aside Jenson Brooksby, who is on the way back from a doping suspension, 6-2, 6-0, 6-3 on John Cain Arena.
In-form Gauff laid down a marker as she swept aside former champion and fellow American Sofia Kenin in straight sets on Rod Laver Arena.
Thunder and lightning saw players and fans rushing for cover, with the heavy rain a headache for organisers who face a match backlog.
The first Grand Slam of the year gets under way at Melbourne Park as a 15-day event for the second year running, aimed at cutting down on late-night finishes.
The British player, who faces a tough first round match against Russian 26th seed Ekaterina Alexandrova, was speaking in the wake of high-profile doping cases involving Iga Swiatak and Jannik Sinner.
Alcaraz won the French Open and Wimbledon titles last year while Sinner claimed the Australian Open and U.S. Open trophies as the pair heralded a new era for the men's game by shutting out 24-times Grand Slam champion Novak Djokovic.
Former world number one Novak Djokovic's Australian Open preparations suffered a blow Friday as he was bundled out of the Brisbane International by towering American Reilly Opelka.
Australian Open champion Jannik Sinner powered to his first Rotterdam Open title on Sunday, breaking down a determined defensive effort from Australia's Alex De Minaur to win 7-5, 6-4 in a high-quality battle.
Patience is a virtue that Sinner does possess, and eventually that paid off.
"I'm the same boy I was before I won the title," he insisted on his return to Rome.
