Sri Lanka have set a target of 160 for Bangladesh to chase at R. Premadasa Stadium in Colombo on Friday.
Sri Lanka managed to score 159 runs losing 7 wickets in 20 overs.
Earlier, Bangladesh have won the toss and have opted to field in their fourth match of the Nidahas Trophy tri-nation T20I series.
Bangladesh cricket superstar Sakib al Hasan, who made a comeback in the squad, gave the Tigers the first breakthrough as he removed opener Danushka Gunathilaka for four in the third over.
Mustafiz dismissed Kusal Mendis (11) and Dasun Shanaka (0) in between his three deliveries in two overs and Upul Tharanga was run out for five in the middle of these wickets.
On the other hand, Kusal Perera and Thisara Perera struck fifties as Sri Lanka recovered from 41-5 to score 159-7 against Bangladesh in the crucial encounter of Nidahas Trophy in Colombo on Friday.
Perera made 61 off 40 balls while Thisara hit 58 off 37 balls as the pair added 97 runs for the sixth wicket to help Sri Lanka scoring a challenging total after they were sent to bat first.
Bangladesh: 1 Tamim Iqbal, 2 Soumya Sarkar, 3 Liton Das, 4 Mushfiqur Rahim (wk), 5 Mahmudullah, 6 Shakib Al Hasan (capt), 7 Sabbir Rahman, 8 Mehidy Hasan, 9 Mustafizur Rahman, 10 Rubel Hossain, 11 Nazmul Islam
Sri Lanka: 1 Danushka Gunathilaka, 2 Kusal Mendis, 3 Kusal Perera (wk), 4 Upul Tharanga, 5 Thisara Perera (capt), 6 Dasun Shanaka, 7 Jeevan Mendis, 8 Akila Dananjaya, 9 Isuru Udana, 10 Amila Aponso, 11 Nuwan Pradeep