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.
Rafael Nadal claimed a dominant straight-sets win over world number three Milos Raonic to advance to the semifinals at the Australian Open on Wednesday.
Former champion Stan Wawrinka engaged in a war of words with Jo-Wilfried Tsonga but won the argument that counted to storm into the Australian Open semi-finals with a 7-6(2) 6-4 6-3 win over the Frenchman on Tuesday.
Venus Williams continued her astonishing late-career revival by felling Anastasia Pavlyuchenkova 6-4 7-6(3) on Tuesday to reach her first Australian Open semi-final in 14 years and become the oldest woman to reach the last four at Melbourne Park in the professional era.
Rafael Nadal's ageing legs outlasted German teenager Alexander Zverev in an epic five sets as Serena Williams sailed into the last 16 at the Australian Open on Saturday.
Andy Murray is yet to reach his maximum potential and should only get better but the world number one has not seen the back of Novak Djokovic, according to eight-times grand slam champion Andre Agassi.
Serena Williams gave compatriot Nicole Gibbs a lesson in grand slam tennis with a 6-1 6-3 towelling to reach the fourth round of the Australian Open on Saturday.
With Novak Djokovic's reign broken, Andy Murray boosted his claim to the Melbourne Park throne with a comprehensive 6-4 6-2 6-4 win over American Sam Querrey to reach the fourth round of the Australian Open on Friday.
Uzbek Denis Istomin pulled off an Australian Open upset for the ages when he sent reigning champion Novak Djokovic tumbling out of the year's first grand slam in a near five-hour epic on Thursday.
Third seed Milos Raonic continued his machine-like advance through the Australian Open on Thursday, easing past Gilles Muller 6-3 6-4 7-6(4) to reach the third round.
Rafael Nadal powered into the second round of the Australian Open with a commanding straight-sets win over Germany's Florian Mayer on Tuesday.
