Deciding to bat, Sri Lanka racked up 312 runs for the loss of only four wickets before bundling out Bangladesh for 186 runs in 40.2 overs.
It was Sri Lanka's second win in the tournament after narrowly beating Pakistan by 16 runs in their opening encounter.
Sri Lanka dominated the game right from the start. Dilshan, who smashed 71 off 51 balls with the help of 11 fours and one six, came back to take three Bangladesh wickets with his off-spin, dealing crucial blows to the top and middle order.
In Image: Bangladesh's Syed Rasel, left in green, and Naeem Islam, right, congratulate Sri Lankan team