Gabon were defeated 4-2 on penalties by Thailand following a 0-0 draw in the semi final of the King's Cup in Bangkok on Thursday.
The Panthers struggled to forge chances in the absence of their talismanic forward Pierre-Emerick Aubameyang, while Thailand created a lot but were unable to open the scoring.
The Arsenal hitman has missed the tournament following the passing of his grandmother.
However, goalkeeper Kawin Thamsatchanan saved Gabon's first two spot kicks during the shootout as the War Elephants won 4-2 in front of 25,000 at the Rajamangala National Stadium.
The win sends Thailand through to Sunday's final meeting with Slovakia, who defeated the United Arab Emirates 2-1 earlier this week. Gabon will meet the UAE in a third-placed playoff earlier in the day.
Milovan Rajevac, the coach of two-time King's Cup winners Thailand, has experience of African football following a memorable spell with the Ghanaian national side and a less successful stint with Algeria.
Jose-Antonio Camacho's Central Africans are using this tournament as part of their preparations for the 2019 African Cup of Nations qualifying campaign after being pipped to a spot at the 2018 World Cup by Morocco.
They've been drawn alongside Burundi, Mali and South Sudan in CAF qualifying Group C as they look to reach next summer's showpiece in Cameroon.