Sri Lanka 5 for 138 (Mathews 35*) beat Australia 3 for 137 (Warner 90*, Voges 25*) by 5 wickets
Live scorecard and ball-by-ball details
Sri Lanka's collective effort was enough to overcome an Australian team that left far too much up to David Warner on their National Day with the visitors claiming a five-wicket victory on a pudding of a drop-in pitch at Sydney's Olympic Stadium.
After their bowlers had been brilliantly supported in the field to restrict Australia to 3 for 137 - of which Warner made no fewer than 90 - the Sri Lankans made a rapid start to the chase and then steadied against the loss of mid-innings wickets to take a 1-0 lead with seven balls to spare.
Angelo Mathews showed the cool head that has him marked as his nation's long-term leader to finish off the innings. There were cameos, too, from Kushal Perera, Lahiru Thirimanne and Thisara Perera, all of whom will be happy that Sri Lanka cannot now lose this series after also tying the ODI matches.
Nuwan Kulasekara and Thisara Perera were both exemplary with the ball, though Kulasekara undid much of his good work by turfing the simplest of chances at deep midwicket when Warner had made only 69.
While there was no switch-hit of the kind he managed in this fixture against India last year, Warner's controlled aggression to bat through the innings was all the more admirable for the difficult surface on which he demonstrated it, and the relative lack of prowess shown by the rest.
Aaron Finch was again out cheaply at international level, while Shaun Marsh made an unhappy return to the national team in his first match since last summer, run out for only six. George Bailey also failed to make a score, leaving Adam Voges to offer inconspicuous but valuable support to Warner, who found it far easier than his team-mates to split the field and find the boundary.
Sri Lanka's pursuit began with speed and audacity, Tillakaratne Dilshan executed one of his trademark scoops from the bowling of Mitchell Starc so effectively that it sailed for six a few metres to the offside of the wicketkeeper. Kushal Perera was more orthodox, but struck the ball cleanly as Australia cast around for a momentum changer.
They found it in Ben Laughlin, recalled for his first T20 international since 2009. Known primarily for his slower ball variations, Laughlin squeezed a bouncer past Dilshan and into the gap between helmet and grille, forcing a delay while a cut above the eye was treated. The break disrupted Sri Lanka's flow, and it was Laughlin who took advantage in the field sprawling to grasp a Dilshan half-chance from Xavier Doherty.
The surface's sluggishness lent itself to bowlers not offering much pace, and Glenn Maxwell's introduction brought further wickets. Kushal Perera snicked an attempted cut behind, and Dinesh Chandimal was held at long off. Mahela Jayawardene played all around a flighted ball from Doherty, and when Thirimanne sliced Mitchell Starc to backward point the chase was drifting.
But Mathews played with calm and precision, while his opposite number Bailey seemed to miss a couple of tricks by not using Maxwell's full quota and also not calling on the quite respectable left-arm spin of Voges.
Laughlin's earlier heroics were to be overshadowed as Mathews took to him for critical boundaries to cut the target down, and Thisara Perera ended the contest with a pair of sixes from the same bowler, delighting the Sri Lankan minority in a crowd of 40,242.
Australia's earlier progress was laborious, the batsmen struggling for timing on a drop-in pitch that offered them little in the way of consistent pace. Finch's stay was ended when he tried to turn Kulasekara to the legside and proffered a front edge that was nicely held by Kushal Perera.
Marsh was soon back at the boundary's edge himself, run out by Dilshan's underarm after turning back on the most optimistic of singles, but Warner endured. Recognising the slowness of the surface, he stayed on the back foot for much of the time, punching shorter balls through the offside and only swinging straight at the fullest of deliveries.
It proved an effective method and, after Bailey perished to another mistimed stroke, Voges hung in to allow Warner to push Australia to a better total than they might have imagined at 3 for 53 after nine overs. Nonetheless, a total of 137 looked slim, and so it was to prove.