Adelaide: Tillakaratne Dilshan led the way with an impressive century as Sri Lanka humbled Australia in an eight-wicket win on Tuesday to force the Tri-series into a third and deciding final.Dilshan shared a 179-run opening stand with skipper Mahela Jayawardene (80) and a 55-run second-wicket partnership with Kumar Sangakkara before he was caught in the outfield off Brett Lee's bowling in the 38th over, with the Sri Lankans needing only 38 runs for victory.Sangakkara finished unbeaten on 51 when he hit the winning boundary with almost six overs to spare.Australia posted 271-6 after winning the toss and batting, with David Warner scoring 100 and Michael Clarke belting 117 from 91 balls before Lasith Malinga took three late wickets to give Sri Lanka some momentum.It was Warner's second century in three days, following his 163 in Australia's 15-run win in the first final on Sunday, but it was uncharacteristic â coming off 140 balls and containing only a sprinkling of boundaries.Clarke dominated the 184-run third-wicket partnership with Warner, stroking five boundaries and four sixes as he tried to lift the sluggish runrate, but also injured his left hamstring and is in doubt for the third final at Adelaide Oval on Thursday."We didn't score enough runs, our fielding was poor again tonight and our bowling let us down," Clarke said. "On a very good batting wicket, against a good and strong batting opposition, you need to make 300 on that wicket."The Sri Lankans also had problems in the field, dropping five catches, but bowled with more discipline than the Australians after opening with offspinner Dilshan in a surprising move by Jayawardene. Malinga's bowling in the end, when Australia could only muster 35 runs in the last five overs, was critical to Sri Lanka leveling the series.Australia had been in command of the first final, having Sri Lanka struggling at 144-6 chasing 322 for victory in Brisbane on Sunday, but slumped in the last 20 overs against an onslaught from the lower-order batsmen and only ended up winning by 15 runs in the last over.Defending a low total on Tuesday, the Australian bowlers again struggled, conceding 30 runs in the first three overs including 11 sundries. The Sri Lankan batsmen took their cue from there, and kept the runrate up throughout the innings."We bowled really well up front, kept them to a reasonable total. With the bat, we had a very positive start, said Jayawardene, who was sanctioned by the match referee for arguing a no-ball call by the umpires during the Australian innings.The Sri Lankans have won four of their last five matches against Australia and overcame two early losses in the tournament to edge World Cup champion India for a place in the final.Jayawardene said his team, runnersup at the 2011 World Cup, had proved its critics wrong."No one gave us any chance when we came to Australia," he said. "As long as we're confident about our game, and play the way we've been playing the last couple of weeks, we've got a very good chance."