Kusal Mendis was the hero of the run-chase for Sri Lanka with a 37-ball 60, but he could have been dismissed a lot earlier had it not been for huge slice of luck going his way. Mendis had four clear chances, and thanks to ESPNcricinfo's Luck Index, we can quantify the impact of those chances, in terms of the runs they cost Bangladesh.
The most expensive of those lives was the first one, which came in the second over of the innings, when Mendis had scored just 2 off 3 balls. Mushfiqur Rahim dropped a tough catch off Taskin Ahmed, and according to Luck Index, it cost them a whopping 37 runs. In short, had that chance been taken, Bangladesh would have almost certainly won the game.
Bangladesh had three other opportunities to dismiss Mendis, but failed each time. In the seventh over, he was caught-behind off a no-ball when on 29 off 16. That cost Bangladesh 10 runs, while the non-review of a caught-behind (which was called a wide) cost them seven runs.
These values are calculated through a complex algorithm which assumes that the batter would have been dismissed off the ball he survived, and simulates the rest of the innings by allocating the extra balls played by that batter to the others who were either unbeaten or didn't bat in the innings.
In this case, since Sri Lanka lost eight wickets in chasing down the target, there were only three batters to whom those extra deliveries could be allocated - Maheesh Theekshana and Asitha Fernando, who were unbeaten, and Dilshan Madushanka, who didn't bat. Given that they are all lower-order batters, the algorithm suggests that Sri Lanka would have been bowled out had Mushfiqur taken that chance to dismiss Mendis early, and they would have only scored 21 runs off the 34 extra deliveries, instead of the 58 that Mendis ended up scoring.
Mendis did eventually fall to a terrific catch by Taskin, but the extra runs he scored almost certainly cost Bangladesh the game.