Forty-eight off 18 balls became 36 off 12, and then came the over that turned things firmly in Sri Lanka's favour. Moises Henriques, who earlier had struck an unbeaten half-century to set Sri Lanka a target of 174, failed to find the right lengths and was plundered for three consecutive sixes by Gunaratne, as well as a four, and it left them requiring 14 from the final over, to be bowled by Andrew Tye.
Although Tye struck with the first ball - Nuwan Kulasekara caught skying a slog - the batsmen had crossed, and Gunaratne was back on strike. Full toss, four down the ground. Six over mid-off. And then, surprisingly, a single, which brought Lasith Malinga on strike needing three off two. Malinga found the single he needed, and Gunaratne crunched the match-winning four over cover, to finish unbeaten on 84 from 46 deliveries.
The Sri Lankan squad poured onto Kardinia Park to celebrate winning the series in front of a 13,647-strong crowd, a hefty percentage of which were Sri Lankan fans. Remarkably, the win meant Sri Lanka held a 5-0 record over Australia in T20s in Australia. The best Australia can now hope for is to make that 5-1 after the third match of the series at Adelaide Oval this Wednesday.
Yet for most of the chase, Australia appeared to be in control. They had Sri Lanka five down within five overs. The rain that both sides feared might affect the game had stayed away, but still it was threatening to become a damp squib. Tye had struck twice in an over, the debutant Jhye Richardson claimed a wicket with his third ball of international cricket, and Ashton Turner had got rid of Sri Lanka's captain Upul Tharanga in the very first over of the innings.
But the small boundaries meant that while Gunaratne remained, Sri Lanka were never out of the contest. He began the rebuild with a 52-run stand with Chamara Kapugedara, which ended when Kapugedara was well caught by Ben Dunk, leaping at mid-off like an AFL player taking a mark above his head. Still, Gunaratne had enough partners, though Australia's captain Aaron Finch conceded after the match that his team had done too little to keep Gunaratne off strike.
Slowly at first and then quickly at the end, he had brought Sri Lanka back into the game. Their bowlers, though, had helped by restricting Australia in the final few overs of the first innings. Australia had cruised to 2 for 111 after 13 overs, the kind of platform from which a total nearing 200 could be achieved, but Sri Lanka found a way to halt the momentum and Australia were bowled out for 173 from the last ball of the 20th over.
The runs came largely at the top of the order - nobody outside the top four reached double-figures. Henriques, whose eight T20Is have been spread fairly evenly over eight years, made an unbeaten 56; Michael Klinger, playing his first international series at the age of 36, scored a composed 43; Dunk, a regular run-basher in the BBL, completed a whirlwind cameo of 32 off 14. But as the batsmen departed, the runs slowed, and only 14 came off the final two overs for the loss of four wickets.
Malinga picked up two important late wickets, trapping both James Faulkner and Tim Paine lbw cheaply, and Nuwan Kulasekara struck three times in the final over of the innings. Australia had needed one of their established men to stick around until the end, but the innings petered out. After Sri Lanka's early stumbles, the match itself looked like petering out too. Only Gunaratne knew differently.