Stephens, the reigning US Open champion, overcame French Open holder Ostapenko 7-6, 6-1 at the Crandon Park Tennis Centre in WTA Premier Mandatory tournament.

The triumph for the 25-year-old from Florida kept up her remarkable unbeaten record in tournament finals.

Stephens will also enter the top 10 of the world rankings for the first time in her career as she will become the world number nine when the updated list is released tomorrow.

"I wasn't expecting a title here or anywhere, really," said Stephens.

"I just wanted to make sure I got my game back where I wanted it to be.

"I knew if I just got back to the drawing board I would be okay."

The first set was a tense affair between two players who had never met on court before.

Four consecutive breaks of serve greeted the start of the first set, which eventually went to a tie-break.

Having dropped the opener, sixth seed Ostapenko recovered and broke Stephens in the first game of the second set.

It proved to be a fleeting moment of success for the Latvian, however, as the 13th seed won six straight games to wrap up a commanding victory.

"I was a little nervous and it was showing in my game," Stephens said.

"My feet weren't moving and I wasn't swinging good at the ball.

"I just needed a little reminder to go for my shots, go for my forehand and really go for it if I wanted to take the title."

The tournament in Miami is due to conclude tomorrow with the men's final of the ATP World Tour Masters 1000 event between American John Isner and Germany's Alexander Zverev.