Radwanska, the fifth seed, needed one hour and 44 minutes to seal her triumph.

The Pole, who also took the title in Dubai earlier in 2012, will now move up to a career-high position of four in the world rankings.

It was a victory Radwanska founded on her own serve. Second seed Sharapova, who has now lost all four of her final appearances at the Miami event, failed to break once in the match.

Radwanska was content to keep the ball in play and wait for Sharapova to make the first mistake. It proved a shrewd tactic as the Russian committed 45 unforced errors in all.

"I got a lot of good wins this year against top players," said Radwanska, who is now 26-4 for the year, all four defeats coming against world number one Victoria Azarenka.

"I was trying from the beginning to focus on my serve, put my first serve in and go for it.

"I think I did a really good job today and the serve was the key."

Loose shots

The first set was heading to a tie-break when Sharapova, down 6-5, suddenly lost her previously solid service game.

Sharapova produced two loose shots and then a volley into the net to leave her trailing 0-40 and although Radwanska wobbled with two tame returns into the net, Sharapova failed to clear the net herself to hand her opponent the set.

And the second set followed a similar pattern - both players solid on serve but Radwanska coming out on top when it mattered.

Radwanska fought back from 0-30 down to go 6-5 up and force Sharapova to hold serve to stay in the match.

The Russian looked agitated and was let down by some reckless strokes, twice going long on returns, as Radwanska lured her into defeat.