BANGKOK - Surprise qualifiers Vietnam dented Thailand's hopes of a fourth Southeast Asian championship title with a stunning 2-1 away win in the first leg of the final on Wednesday. The victory sparked wild celebrations in Hanoi, with the streets gridlocked as cheering fans waved national flags and motorcyclists sounded their horns. In their first final in a decade, Vietnam soaked up a torrent of early attacks before scoring twice in three minutes to grab the advantage ahead of Sunday's home return. Le Tan Tai caught the Thai defence napping in the 40th minute when he crossed to the unmarked Nguyen Vu Phong, who delivered a perfect header into the bottom corner of the net from six metres. Peter Reid's misfiring side then conceded a second goal when Nguyen Viet Thang set up Le Cong Vinh. Thailand pulled one back in the 75th minute when substitute Ronnachai Rangsiyo's header struck the post before going in off the leg of goalkeeper Duong Hong Son. GOAL DISALLOWED Arthit Sunthornphit twice went close to an equaliser, having a goal disallowed for offside and forcing a good save from Hong Son. "We're only halfway there but I believe with heart that the weak team can beat the stronger team," Vietnam coach Henrique Calisto told reporters. "I'm very proud of these players, they believe in themselves, they're proud to play for this team and their country." It was the first competitive defeat for Reid since he took over as coach four months ago. "We were a little bit naive and paid the penalty," said the former England midfielder. "We've now got to fight hard but it's far from over."