Azarenka's joy saw her burst into floods of tears after securing a second Grand Slam title, while Li added the pain of failure to the physical pain she endured during the match.
The Chinese star's efforts were undermined by two dramatic incidents: a sickening ankle injury in the second set, and a fall in the final stages which sparked concussion fears as she hit her head on the court as well as twisting her ankle a second time.
Li dominated the first set but Azarenka raced out to a 3-1 lead in the second before Li slipped and twisted her left ankle.
She had it strapped but had problems pivoting and Azarenka won the set 6-4.
The Chinese sixth seed, who won the French Open title in 2011, took a 2-1 lead in the decider before an Australia Day fireworks display delayed play for some 10 minutes. She immediately went over on her ankle again when they returned and hit her head.
A smiling Li returned to court but Azarenka managed to break in the fifth game, then hold serve to jump to a 4-2 lead and she sealed the title, which ensured she retained the world number one ranking, when she broke Li in the ninth game.
Azarenka dropped her racket to the ground and, after shaking hands with Li and the umpire Alison Lang, went tearfully to her players' box where she was embraced by her support staff and friends who included American musician Redfoo.
Perhaps weighed down by expectation from the most populous nation in the world and with an estimated 100 million people watching on television in China, Li had a shaky start, serving a double fault on the first point and having her serve broken.
The world number six, however, bounced straight back to the delight of the overwhelmingly pro-Li crowd in Rod Laver Arena and used her powerful forehand to break Azarenka twice to hold a 3-1 lead.
Azarenka battled back to break to reduce the deficit to 3-2, but was broken again by Li, who was relentlessly attacking the Belarussian's serve.
Azarenka was able to hold for the first time in the eighth game and break in the ninth, but Li broke again on her fourth set point when the Belarussian double faulted to take the first set 6-4.
Azarenka finally found her range with her groundstrokes in the second set and moved a lot better to race out to a 3-0 lead.
Li broke back, but then badly hurt her ankle after she was forced to change direction to try to reach an Azarenka backhand volley.
The Chinese took a medical timeout to have the ankle heavily strapped but held serve on her return and got three break points in the next game as both players tightened up and were seemingly unable to hold serve.
Li was broken again in the ninth game to give Azarenka a 5-4 lead and she served out to love in the next game to send it into a decider when a Li forehand sailed wide.
Both had problems settling again after the interruptions to the third set but Azarenka achieved the crucial break and was able to hold things together long enough to earn her second grand-slam title when a Li forehand sailed long over the baseline.