Sri Lanka, chasing a revised target of 238 in 41 overs following a power failure, won the day-night match with 32 balls to spare.
Earlier, Tamim Iqbal smashed an impressive century as Bangladesh posted a competitive 259-8. The left-handed opener (112) hit one six and 10 fours in his fourth one-day hundred to lead Bangladesh's recovery after three wickets had fallen for 63 runs in the opening 13 overs.
Tamim put on 66 for the fourth wicket with Mohd Mahmudullah (29) and 75 for the next with Nasir Hossain (73 not out).
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