Mahmudullah (43 not out) struck a stunning six in the penultimate delivery to reach to the target of 160 to the wild celebration of the Bangladesh camp after tempers were frayed due to debatable decisions from the umpires.

The match at the R Premadasa Stadium was marred by drama at the fag end of the virtual semifinal as Bangladesh captain Shakib Al Hasan gestured to his two batsmen to come out of the field apparently in protest against giving a run-out decision to Mustafizur Rahman on a seemingly shoulder-height ball.

But better sense prevailed in the end after arguments between the players of the two sides and intervention by match officials.

Bangladesh, who have also beaten the same opponents earlier in the tournament, secured four points from four matches to enter the final.

India, with six points from four matches, have already qualified for the summit clash to be played at R Premadasa Stadium on Sunday. Sri Lanka finished last with two points.

Chasing a target of 160, Bangladesh were nicely placed at 80 for 2 at the halfway stage but they lost their way after that as their three key batsmen -- Mushfiqur Rahim (28), Tamim Iqbal (50) and Soumya Sarkar (10) -- fell one after the other in the next three overs as Sri Lanka sought to turn the tables in the second half of the innings.

But it was still a chaseable target as Bangladesh needed 30 runs from three overs with captain Shakib Al Hasan (7) and Mahmudullah at the crease.

But the departure of Shakib, who was playing his first match of the tournament after sitting out due to a finger injury, in the 18th over made matters difficult for Bangladesh.

But Mahmudullah kept his nerve and after a brief period of frayed tempers took his side home.

Bangladesh needed 12 from the final over but Mustafizur Rahman (2) was given run out in the second ball which triggered a wave of wild protests both from Mahmadullah and the team bench beyond the ropes.

After the matters were sorted out, Mahmadullah hit the third ball of the final over for a boundary and then hoisted Isuru Udana for a six to snatch victory from the jaws of defeat.

Earlier, captain Thisara Perera and Kusal Perera struck half centuries in a fine counter-attacking batting display as Sri Lanka recovered from a top-order batting collapse to post a competitive 159 for 7.

Put into bat, Sri Lanka were in all sort of trouble early in their innings against the Bangladeshi bowlers, led by young left-arm pacer Mustafizur Rahman whose incisive pace spell rocked the home side batsmen.

But the Perera duo, Thisara (58) and Kusal (61) showed their mettle with a fine counter-attacking batting display to take their side past the 150-run mark. put on a crucial 97-run stand with stand-in skipper Thisara, who hit 58.

Sri Lanka were 41 for 5 in the ninth over and they were staring at a meagre total but Thisara and Kusal had other ideas as the duo flayed the Bangladesh bowlers at the later stages of their innings.

Kusal, who scored his third half century of the tournament, needed 40 deliveries for his 61. He hit seven fours and one six. Thisara, on the other hand, faced 37 balls for his 58 and struck three fours and as many sixes.   

Both Kusal and Thisara hit the bowlers to all parts of the ground at the R Premadasa Stadium, hitting 10 fours and four sixes between them.

Bangladesh were, however, on top initially with their bowlers, led by Mustafizur Rahman (2/39), creating havoc on the home side top-order batsmen.

The 22-year-old Mustafizur, who was bought by Mumbai Indians for Rs 2.2 crores for the upcoming IPL season, had in-form Kushal Mendis (11) in the fourth over and then dimissed Dasun Shanaka (0) in his next over.  At one stage, his figures read 2-1-4-2.

Bangladesh captain Shakib Al Hasan gave the first breakthrough by claiming opener Danushka Gunathilaka (4). Shakib struck in his comeback after he made it to the team after sitting out of the previous matches due to to a finger injury.

Mustafizur was also involved in the run out of Upul Tharanga (5) in his second over, as the sixth over yielded two wickets.

The back of Sri Lankan batting was broken by the end of powerplay overs as they were reduced to 35 for 4 at the end of sixth over.

Mehidy Hasan Miraz joined the party by removing Jeevan Mendis in the ninth over as Sri Lanka lost half of their batsmen for just 41 runs. This was before Thisara and Kusal resurrected the Sri Lankan innings with a stunning batting display.