Sharapova was bidding to become the first woman to win back-to-back titles at Indian Wells and Miami could barely have played better for a set and a half.
But still Williams managed to find a way through as she became just the fourth woman to win one title six times and the first in Miami.
The only other women to achieve the feat are Martina Navratilova (who won an incredible nine titles six times or more, including nine Wimbledon trophies), Steffi Graf (who won six titles six times or more, including seven Wimbledons and six French Opens) and Chris Evert (who won five titles six times or more, including seven French Opens and six US Opens).
Sharapova had lost the previous 10 encounters against Serena, a fact that the Russian was clearly aware of as she made a aggressive start to the match.
The tactic proved almost immediately fruitful, Sharapova earning herself early break points in just the third game of the match before going on to break two games later.
Williams cancelled that out in the very next game but Sharapova was determined not to be put off and re-established her break lead in the ninth game, pushing the American around the baseline and eventually drawing the error.
That break left Sharapova serving for the opening set, something she reeled off with panache, the Russian serving out to love for her first set against Williams in five years.
Williams made a move to dampen Sharapova’s momentum early in the second set breaking in just the second game as both players struggled with the sun down one end of the court.
Sharapova broke back immediately and then even took the lead, breaking to love in the fifth game, only to drop her serve in the sixth, also to love, as the sun continued to wreak havoc for the server.
An inspirational return game from Williams in the eighth game saw her finally get the chance to level the match; the American applying so much pressure to her opponent’s serve that Sharapova slapped down a double fault and netted a forehand on her way to conceding.
Serving from the end where the sun was causing the server most problems, Williams quickly went 0-30 down as she looked to level the match. But sheer determination saw the world number one through as she recovered to fashion a set point with an ace before Sharapova sent a forehand long as the set slipped by.
"I was just making so many errors, and I just was like, 'Serena, are you really going to get to the final and not play up to your potential?'" said Williams.
"I was losing a little bit of pace on my ball which hurt me," said Sharapova. "Against a player like Serena, you can't really do that."
Williams, who has 15 Grand Slam singles titles, was happy to claim the record but was far from satisfied with her performance.
"One of the first things I said (after the match) is I need that tape so I can go home and study it and train and try to get better," she said.
From there it was mainly one-way traffic, Williams subjecting Sharapova to a bagel in the final set despite the Russian doing very little wrong.
By that stage, however, Williams had the trophy (and Miami record) in her sights and rattled through the final six games to wrap up the match in two hours and nine minutes.
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