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.
Serena Williams exploded any doubts about her form on Tuesday as she swept into the Australian Open second round on her return to Grand Slam action.
Venus Williams survived a rocky start to reach the second round of her 17th Australian Open on Monday, putting her 7-6 7-5 victory over Kateryna Kozlova down to hard-earned experience.
World number one Andy Murray could face challenges from Kei Nishikori and Stan Wawrinka if he is to reach a sixth Australian Open final following Friday's draw.
Next month's Australian Open will offer Aus$50 million (US$36.25 million) in prize money, with the men's and women's singles champions both netting a cool $3.7 million, organisers said on Wednesday.
Maria Sharapova is suspended for two years by the International Tennis Federation for testing positive for meldonium at the Australian Open.
Nike suspends its relationship with Maria Sharapova after the five-time Grand Slam tennis champion admitted failing a drug test.
Former world number one Maria Sharapova has revealed she failed a drugs test at the Australian Open.
Tennis star Andy Murray's wife Kim Sears gives birth to a girl, who is thought to have arrived on Sunday night.
World number one Novak Djokovic beat Andy Murray in straight sets to win his sixth Australian Open title and condemn the Briton to a fifth final defeat.
World number one and defending champion Serena Williams will face Maria Sharapova in the Australian Open quarter-final.
