Maria Sharapova extended her unwelcome record of losing in the Sony Open final as the world number one came back from a set down to power to victory.
Sharapova left empty handed in Miami again as Williams battles back to win record sixth title
The world number one went down 4-6 to Sharapova, who has never won Miami despite five finals appearances, before powering back 6-3 6-0.
The result makes Williams becomes only the fourth woman in the Open era to win the same WTA tournament six times, putting her in the company of Martina Navratilova, Chris Evert and Steffi Graf.
"It's so good to win number six," Williams said afterwards.
"Start of the tournament, I definitely didn't feel like I would be here, not with the way I was playing. But it definitely feels good to go through everything.
"I'm happy to be here holding the championship. It's definitely not my best tournament but the moments that count is when you can go and do the best you can and still come out on top and always try to improve."
It was the 11th match victory in a row for Williams over Sharapova, with the 31-year-old American now boasting a 12-2 edge in their rivalry.
"She definitely pushed me," Williams said. "I definitely look forward to our next matches."
The Russian, who won at Indian Wells earlier this month, took her great form into the opening set, almost breaking Williams in a marathon third game featuring some outstanding baseline rallies.
Sharapova, playing sparkling all-round tennis, got her reward when she broke to go 3-2, with a powerful backhand shot that Williams could only return to the net.
Williams broke back straight away though, but a confident Sharapova took advantage of some over-hitting from the American to break in the ninth game and served out to win the set.
It looked as though Sharapova had a real chance to finally end her nine-year winless streak against the American but, as so often, Williams refound her game in the second.
After some entertaining exchanges, a double-fault from Sharapova handed Williams a break point and the Russian's return to the net gave Williams a 5-3 lead and she held to force the third set.
The match turned decisively in Williams' favour when Sharapova produced two double-faults to go down 3-0 in the third set and the Russian never was able to claw back from that position.
"I certainly put myself in a much better position today," Sharapova said afterwards
"I had my chances. There's no reason why I couldn't win the match. I was playing, not well enough to win the match, obviously, but it was a step in the right direction and there's no doubt that we'll be playing many more times.
"There's no doubt I'll be able to beat her."
Follow us @SprtNationalUAE