Fabian Allen has hit three mighty sixes in the 19th over to help the West Indies to a series-clinching, three-wicket win over Sri Lanka in the third Twenty20 international.

Chasing a modest 4-131, the West Indies were again constrained by Sri Lanka's spin attack and came to the 18th over at 7-105, needing 27 to win from 18 balls.

Captain Jason Holder blocked out the 18th over, the last from dangerous spinner Wanindudu Hasaranga, save for a six from a free hit which helped break the mounting tension.

With 20 runs needed from the last two overs, Allen hit sixes from the first, third and last balls of the 19th over, from Akila Dananjaya, to get the West Indies home with an over to spare to clinch the series 2-1.

Dinesh Chandimal (54no) and Ashen Bandara (44no) had been the pick of the batsmen for Sri Lanka, producing an unbroken partnership of 85 from 63 balls to lift their side to a low-scoring 4-131.

Allen hit 21 runs from six balls and also took 1-13 from four overs to earn player-of-the-match honours.

He said there was no panic in the West Indies dressing room, even when the biggest hitters failed to fire.

"We have a lot of batting power," Allen said.

"I told Jason Holder that I'm not comfortable batting against Hasaranga. So I told him to bat him out and I'll be finishing.

"I just backed myself in the end. It was a good performance overall."

The first of three one-day internationals between the teams begins at the Sir Vivian Richards Stadium in Antigua on Thursday.