Chasing 133 to win, Sri Lanka registered their first win over Pakistan in the new-style, wham-bang format with six balls to spare.
He may be pushing 40 years old but Jayasuriya (40 runs) showed little sign of ageing as he and fellow opener Mahela Udawatte (25) put on 66 in 6.6 overs.
They took advantage off a wayward Pakistan attack with Shoaib Akhtar, Sohail Tanvir and Umar Gul being hit to all parts of the ground in front of 9,000 fans at King City.
Jayasuriya was particularly harsh on Akhtar, flicking the recalled quick for four in his first over and then pulling him for consecutive sixes over midwicket.
Desperate Pakistan, who had won the group match between the two sides by three wickets on Saturday, turned to spin and Shahid Afridi dismissed Udawatte while Shoaib Malik accounted for Jayasuriya.
But despite losing skipper Mahela Jayawardene for just five, Kaushalya Weeraratne (12) and Chamara Kapugedera (17 not out) saw Sri Lanka home.
Earlier Mendis, 16 years Jayasuriya's junior, took 3-23 for a tournament total of 11 wickets as he put the brakes on the Pakistan middle order.
Opener Salman Butt top scored with 44 before he fell to Mendis who also accounted for Shoaib Malik and Kamran Akmal. Zimbabwe trounced Canada by 109 runs to claim third place.
Zimbabwe had needed a bowl-out to beat the hosts in the group stage on Saturday but there was no repeat of that drama this time as the African side piled up 184-5, the highest score of the tournament.
Opener Hamilton Masakadza smashed 79 with useful contributions coming from Chamu Chibhabha (40), Elton Chigumbura (25) and Keith Dabengwa (16 not out).
Masakadza had made a brave 53 in his side's seven-wicket loss to Pakistan on Saturday and he was in brutal form again on Monday smashing two giant sixes off Abdool Samad.
Canada were immediately in trouble slipping to 10-3 by the sixth over as captain Ashif Mulla (2), Rizwan Cheema (2) and Sandeep Jyoti (0) all failed.
Canada just managed to avoid the lowest Twenty20 score of all time - Kenya's 67 against Ireland in August - as they were skittled out for 75 with Zimbabwe's 23-year-old captain Prosper Utseya taking 3 for 26 with his off-breaks.