It was Williams' sixth title at Melbourne Park and it moved her into a tie with fellow American Helen Wills Moody in third on the all-time list after she joined Martina Navratilova and Chris Evert on 18 at last year's U.S. Open.
Only Australia's Margaret Court (24) and Germany's Steffi Graf (22), who holds the record for the Open era, have more grand slam singles titles than the 33-year-old American.
Williams had not lost to Sharapova since the 2004 WTA Finals, a run of 15 successive victories and was not about to let the Russian end that streak on Saturday.
After Williams snatched a break in the first game, rain forced the players off court in the sixth for 12 minutes as officials closed the roof with the American serving at 3-2 and the score locked at 30-30.
Williams, who has been battling a cold and cough the entire tournament, chose to head inside during the break while Sharapova waited courtside. She returned to Rod Laver Arena hacking like a seal and appeared to be gasping for breath, but then reeled off the next six points to establish a 5-2 lead.
While Sharapova managed to break in the next game she was unable to consolidate and Williams broke to love to seal the first set in 47 minutes. Williams did not concede a point on serve until her third game of the second set while Sharapova struggled and was fighting to stay in the match.
Even when she had break opportunities in the fifth and seventh games the American simply reached back and smashed down a succession of massive serves. Williams held a match point in the 10th game only for the Russian, who saved two match points in the second round against qualifier Alexandra Panova, to blast a forehand down the line.

The American held two further match points in the tiebreak and thought she had sealed the title when she belted an ace only for umpire Alison Lang to call a let. Williams stood there looking bemused but composed herself to repeat the shot, smacking her 18th ace to win the match.

Latest News from Sports News Desk