Sri Lanka's captain, Angelo Mathews, helped his side beat hosts Bangladesh by three wickets on Thursday to remain unbeaten in the group stages of the Asia Cup.

Bangladesh's openers Anamul Haque and Shamsur Rahman initially justified their captain's decision to bat first and put on a 74-run opening stand.

But Ajantha Mendis made the first incision in the 19th over and that began a top-order collapse. Bangladesh, like they've done before in the tournament, lost five wickets for 45 runs.

Three of their middle-order batsmen managed to get starts but failed to capitalise further. The hosts scored just 204 from their 50 over.

In reply, Sri Lanaka were off to a disastrous start and lost three wickets for eight runs in the first four overs. With inform Kumar Sangakkara and Mahela Jayawardene back in the pavilion, Sri Lanka's young middle order was put to the test.

At 75 for 5, Mathews and PC de Silva joined forces to provide the definitive partnership in the match. The captain did not allow the losses to rattle him and began rebuilding the innings.

The duo's 82-run stand for the sixth wicket proved to be decisive and turned the match in Sri Lanka's favour. When de Silva was dismissed in the 40th over, Sri Lanka was in control and emerged victorious, with an over to spare.

"I was under a little bit of pressure to be honest," Mathews said. "We were losing wickets and had to consolidate. Chaturanga batted beautifully."

"It is a good problem for us (when Malinga comes back). All the bowlers did well. We wanted to try out a few things (against Bangladesh), wanted to chase and see how we go about it. It was not easy once we lost a few wickets. (Mahela) is a big match player and I am sure he will come good for us."