SINGAPORE, Jan 31 (Reuters) - An outburst of Thai petulance rained chaos on the first leg of a bitterly fought ASEAN championships final on Wednesday before hosts Singapore finally clinched a dramatic 2-1 victory.Thailand's late walk-off protest distorted the host supporters' famed "Kallang Roar" into a cacophony of furious jeers as the visiting side for 15 minutes refused to allow a late disputed penalty to be taken. The showdown had been headed for a 1-1 draw when the dubious refereeing decision caused it to boil over with just eight minutes remaining. Malaysian official C.Ravichandran's decision to award a penalty to the hosts after striker Noh Alam Shah had gone down in the penalty area was a red rag to Thailand who stormed off the pitch. After 15 minutes of head-shaking and arm-waving the Thais finally returned to the pitch to a wall of boos. Mustafic Fahrudin stepped up and fired high into the roof of the net as the home fans erupted and a small pocket of yellow-clad Thai supporters squirmed. Moments later the referee blew up and the Thais ran straight to their bench, ignoring the celebrating Singaporeans. Thailand team manager Tawatchai Sajakul defended the protest. 'We have all calmed down now, but there's something seriously wrong about the decision of the referee,' Tawatchai told Reuters. 'We have a right to protest and we needed to get the message across that we have been unfairly treated. 'This is football. We now have to prepare ourselves mentally and physically for the second leg in Bangkok.' Singapore coach Radojko Avramovic was left mystified by the unfolding drama. 'I don't understand what the Thai coach was doing, or what point he was trying to make,' he said. 'I don't think that's right. This is sport; it should be played like sport. 'There were many players in the area. They were pulling our players all the time. Their punishment came in the end,' he told ESPN. The controversial victory was the first time Singapore had managed to beat Thailand over 90 minutes at the National Stadium since 1977 but ultimately proved as noteworthy for scenes of Thai dissent and petulance as for any milestone result. The incident is sure to add more spice to Sunday's second-leg. Singapore are the holders of the trophy -- formerly the Tiger Cup -- having won in 2004. They also lifted the title in 1998. Thailand are the only other winners of the tournament, champions in 1996, 2000 and 2002. Thailand's late antics stole the show on what had been a thrilling, hard-fought contest. Alam Shah had opened the scoring on a balmy night with his 10th goal of the Asian regional tournament. The hosting Lions had been tigerish in defence throughout the first period but a lapse in concentration five minutes after the break undid all their good work when striker Pipat Thonkanya sprung the defence and rounded Lionel Lewis in the Singapore goal before coolly slotting home to level.