Sven-Goran Eriksson suffered his first defeat as Philippines head coach on Sunday as visiting Vietnam secured a 2-1 first-leg advantage in their Asean Football Federation Championship semi-final.
Eriksson, who has signed a five-month contract with the Azkals and will lead them through the Asean Championships before overseeing their first-ever appearance at the Asian Cup in the United Arab Emirates in January, had won two and drawn two of his first four games in charge.
Yet the former England manager's side fell behind after 12 minutes as Nguyen Anh Duc directed a looping header over goalkeeper Michael Falkesgaard and across the line following Doan Van Hau's punt forward.
Patrick Reichelt equalised for the Philippines in first-half stoppage time when he launched himself at Phil Younghusband's cross from the right to side-foot home a close-range volley.
Yet three minutes into the second half, the Vietnamese, tournament winners in 2008, were back in front as Phan Van Duc controlled Nguyen Trong Hoang's ball through the Philippines defence, leaving the striker to slot beyond Falkesgaard.
The teams meet again in Hanoi on Thursday with the Philippines looking to overturn the one-goal deficit to take their place in the final of the regional tournament for the first time.
The winners will take on either Thailand or Malaysia in the final, with the pair due to play the second leg of their semi-final on Wednesday in Bangkok following a 0-0 draw in Kuala Lumpur on Saturday.