Liyanarachchi provided the late charge, blasting 52 off 27 balls, which included six fours and two sixes, to take Business Management School from Sri Lanka to a challenging 191 for 9 after University of Liberal Arts, Bangladesh skipper MD Hasanuzzaman won the toss and elected to bowl first.
Sri Lanka then returned to restrict the visitors to 167-8 in their stipulated 20 overs and become the first host nation to win the crown.
Besides Jayawickrama, Chamika Karunarathne (2/17), Devin Pathmanathan (1/31) and Liyanarachchi (1/26) were among the wickets for Sri Lanka.
Earlier, opening the innings, G Wimaladharma (17) and D M De Silva (32) shared a 27-run stand before the former was caught by Avishek Mitra off Morsalin Mortaza's bowling in the 3rd over.
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De Silva and DM Sarathchandra then took the team past the 50-mark but Arifur Rahman dismissed the new batsman with MD Haque taking the catch in the sixth over just after he had hit a boundary. Janith Liyanage (2) too was run out as Sri Lanka slipped to 61-3 in the 7th over.
Defending 191, Liyanarachchi drew the first blood, dismissing Sabit Hossain (0) in the second ball of their innings but Bangladesh still had a flying start as Avishek Mitra (28) and Hasanuzzaman blasted a couple of fours each in the second over.
Hasanuzzaman clobbered another six and a four as Bangladesh crossed the 50-mark in 4 overs. The duo continue to dominate the bowlers and took the team close to the 100-mark by scoring 20 runs in the 'energiser over' which they took after the mandatory powerplay of first six overs.
Runs dried up after that wicket and soon Hasanuzzaman too perished in the 11th over. MD Haque (12) hit a four but he was stumped in the next delivery. In the next over, Mohammad Rahman (2) was bowled by Devin Pathmanathan as Bangladesh lost half their side at 113-5 in 12th over.
Koshan Jayawickrama then removed Mohammed Islam (3) and Anjum Ahmed (8) as the visitors were reduced to 126-7 in 15 overs. Maraj Niloy (20) and Arifur Rahman (15) tried their bit but it was too little and too late in the end.