Hasan, 21, on List A debut, made 103 off 89 balls with eight fours and five sixes to help Gazi Group put up 303 for 4 in 50 overs. In reply, Prime Bank were bowled out for 197 in 46.3 overs.
Hasan patiently reached 50 off 58 balls, and only unleashed the hits to the leg side or the lashes over off after crossing 70. He got to his century with a hook off Rubel Hossain and punched the air in delight. Mahedi later took 1 for 22 from 10 overs and was named Man of the Match.
Earlier, Anamul Haque and Shamsur Rahman made fifties, adding 113 for the opening wicket. Mahedi added 54 for the second wicket with Anamul before adding another 84 with Saeed Anwar jnr for the third.
Anwar jnr returned to take 3 for 31 in Prime Bank's reply, while Mohammad Sharif and Moinul Islam picked up two each. Only Yasir Ali and Rubel Hossain made headway for Prime Bank, scoring 56 and 45 respectively.
Jubair started off with the big wicket of Hamilton Masakadza, Kalabagan's foreign recruit and their top-scorer with 41, in the 16th over. Jubair took four wickets in his first spell, reducing Kalabagan to 116 for 6 from a promising 78 for 2. He took the last two wickets too, as Kalabagan were skittled out for 140 in 33.1 overs.
An unbeaten 44 from Uday Kaul, Abahani's Indian recruit, then guided them to the target in 28.3 overs.
Batting first, CCS were bowled out for 177 in 49.2 overs, Pinak Ghosh top-scoring with 35. His fellow Under-19 teammates, Mohammad Saifuddin and Saeed Sarkar, also chipped in with thirties. Al-Amin Hossain and Rejaul Karim took three wickets each.
Imtiaz struck 12 fours in his 140-ball knock, and shared a 106-run opening stand with Rony Talukdar (47), the highest scorer in last year's tournament. The win came with 4.4 overs to spare.
Mohammad Isam is ESPNcricinfo's Bangladesh correspondent. @isam84