Victoria Azarenka overcame an injury-hampered Serena Williams to win 6-3 6-1 at the WTA Miami final.
Williams, heavily strapped on her left thigh, never looked fully mobile and was comfortably beaten in 71 minutes by one of the rising talents in the women's game.
The victory, the first top-tier triumph for Azarenka, stopped the American claiming a record sixth title at Key Biscayne.
It was clear from the outset Williams was not 100 percent fit and she said she had considered pulling out of the final.
"I thought about it. I don't like to not play but I definitely thought about it. I thought the warmer I got the better I thought it felt," said Williams, who added she also had an ankle problem that further restricted her movement.
"It was a little difficult moving to the left and a little bit to the right. A little forward was also difficult," she added with a laugh.
Azarenka, who will move up to eighth in the new world rankings, was nervous as she served for the match, producing a double-fault and allowing Williams break point.
However, having secured her third title of the year following victories in Brisbane and Tennessee, she credited increased confidence for her rapid rise into the top 10.
"I've improved almost everything since last year but most of all I am believing in myself a little more, believing I can win tournaments," said the Arizona-based Azarenka.
The Belarussian teenager broke serve to go 2-1 up in the first set but was broken straight back, a sign Williams was up for a scrap.
Eleventh seed Azarenka played intelligently, pushing her opponent wide and looking particularly strong on her forehand as she broke twice at the end of the set.
That appeared to knock the fight out of Williams and there was never any real doubt about the outcome of the second set, a disappointment for the crowd who had hoped for a much closer contest.
Last time the pair met, in the fourth round of the Australian Open, Azarenka won the first set but then retired due to illness.
Saturday's result means Williams remains tied with German Steffi Graf on five victories at the tournament.