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.
Stefanos Tsitsipas will become Greece's first Grand Slam champion and a world number one if he wins the Australian Open final on Sunday -- he will have his father to thank if he does.
Facts and figures ahead of Friday's Australian Open men's semi-finals (x denotes seeding):
Aryna Sabalenka surged into the Australian Open final with a 7-6(1) 6-2 win over unseeded Pole Magda Linette on Thursday to extend the red-hot Belarusian's unbeaten start to the year and book a clash with Elena Rybakina.
Self-described "obnoxious soccer mom" Victoria Azarenka was ordered to take off her Paris St Germain shirt at the Australian Open on Thursday before bowing out of the Grand Slam with a straight sets defeat by Elena Rybakina in the semi-finals.
Novak Djokovic's father has been filmed posing with fans brandishing banned Russian flags at the Australian Open, including one featuring Vladimir Putin, in scenes Ukraine's ambassador Thursday slammed as "a disgrace".
Novak Djokovic can take a step closer to equalling Rafael Nadal's men's record of 22 Grand Slam titles when he faces Andrey Rublev on Wednesday for a place in the Australian Open semi-finals.
Magda Linette reacted with disbelief after continuing her dream run into the semi-finals of the Australian Open on Wednesday with a stunning 6-3 7-5 victory over former world number one Karolina Pliskova.
Aryna Sabalenka reached her maiden Australian Open semifinal with a battling 6-3, 6-2 victory over unseeded Donna Vekic on Wednesday at Rod Laver Arena in a 1hr 49min tussle.
Big-serving Elena Rybakina blasted her way into the Australian Open semi-finals on Tuesday, while Karen Khachanov followed suit in the men's draw after Sebastian Korda suffered a wrist injury.
American Sebastian Korda reached the quarter-finals of a Grand Slam for the first time on Sunday after defeating Poland's Hubert Hurkacz 3-6, 6-3, 6-2, 1-6, 7-6 (10-7) at the Australian Open.
