Kandy, Aug 31 : Sri Lanka opened their Asia Cup campaign with a convincing five-wicket victory over Bangladesh in their Group B match at the Pallekele International Cricket Stadium on Thursday. On a two-paced pitch, young pacer Matheesha Pathirana took career-best figures of 4-32, while the ever-reliant Maheesh Theekshana picked up 2-19 as Bangladesh were bowled out for 164 in 42.4 overs. Spinners Dhananjaya de Silva and Dunith Wellalage kept the Bangladesh batting line in middle overs, never allowing the batters to score freely, though Najmul Hossain Shanto played a valiant hand for Bangladesh with a fine 89. In reply, Sri Lanka were reduced to 43-3, but Charith Asalanka slammed 62 not out, hitting five fours and a six, while Sadeera Samarawickrama made 54, laced with six fours. On their way to making their respective half-centuries, the duo shared a 78-run partnership for the fourth wicket to complete the chase with 11 overs remaining. Electing to bat first, Bangladesh openers Tanzid Hasan Tamim and Mohammad Naim departed inside eight overs. Tanzid's ODI debut ended in him departing for a duck in the second over as Theekshana got the ball to sneak past the bat and hit his back pad to be trapped lbw. On the other hand, Naim skied one to point off the bowling of Dhananjaya in the eighth over. Skipper Shakib Al Hasan went for a cut off a short and wide delivery from Pathirana in the 11th over, but nicked behind to the keeper, leaving Bangladesh at 37-3. Shanto reached his fourth ODI fifty and put on a stand of 59 runs with Towhid Hridoy (20 off 41 balls). But captain Dasun Shanaka trapped Hridoy lbw after taking DRS, followed by Mushfiqur Rahim holing out to the deep third man on a cut-off Pathirana. Shanto then struggled to find company from the other end as Pathirana and Theekshana ran through the lower order. Apart from Shanto and Hridoy, only two other batters reached double digits as Bangladesh crashed from 127-4 to 164 all out, losing their last six wickets for just 37 runs. In the chase, Bangladesh pacers Taskin Ahmed and Shoriful Islam sent back Sri Lanka openers Dimuth Karunaratne and Pathum Nissanka within the first four overs. Taskin castled Karunaratne for just one in the third over, followed by Shoriful finding Nissanka's edge on a short and wide delivery. Kusal Mendis' struggle ended when he was castled by Shakib in the last over of power-play, leaving Sri Lanka in trouble at 43-3. Samarawickrama and Asalanka hung around to bail Sri Lanka out of a tricky situation, reaching their respective half-centuries. Though Bangladesh took out Samarawickrama and Dhananjaya in quick succession, it was too late as Sri Lanka got their 11th consecutive win in ODIs. Bangladesh's next game against Afghanistan on Sunday is now a must-win clash for them to enter the Super Four stage. Brief scores: Bangladesh 164 all out in 42.4 overs (Najmul Hossain Shanto 89, Matheesha Pathirana 4-32, Maheesha Theekshana 2-19) lost to Sri Lanka 165/5 in 39 overs (Charith Asalanka 62 not out, Sadeera Samarawickrama 54; Shakib Al Hasan 2-29, Shoriful Islam 1-23) by five wickets /IANS