Indonesia stunned hosts Thailand 3-1 in the semi-finals of the AFF U23 Championship on Thursday night and set up a final clash against Vietnam on Saturday.
Indonesia took advantage of an out-of-sorts Thailand side to score all three goals in the first half for the win at the Rayong Provincial Stadium.
Just 10 minutes into the game, Indonesia went ahead after striker Jeam Kelly Stroyer fired in a low grounder to beat Thai custodian Siriwat Ingkaew.
Muhammad Ferrari headed the ball into the far post to give the visitors a 2-0 lead after 23 minutes.
Obviously rattled and under pressure, Thailand started to push for their first goal of the game and it came just four minutes later when Chukid Wanpraphao headed in a corner.
But Natcha Promsomboon's own goal gave the Indonesians a 3-1 advantage at half-time.
Several changes to the Thai line-up after the break failed to improve things much as Indonesia defended well to restrict their opponents to several long-range efforts.
"We had about 16 fit players and for that I appreciate their effort against Thailand," said Indonesia coach Shin Tae-Yong.
Thailand coach Issara Sritaro said: "We conceded early and that own goal really affected us. We just could not recover. We cannot blame anyone else but ourselves. The players just could not cope with the pressure."
The Thai U23 side also lost to Indonesia in the SEA Games final in Cambodia in May.
In the other semi-final, defending champions Vietnam beat Malaysia 4-1 at the same venue.