Thailand coach Mano Polking apologised to home fans after the War Elephants failed to reach the King's Cup final following a penalty shoot-out defeat against Malaysia in Chiang Mai on Thursday night.
Malaysia won 5-3 on penalties after a 1-1 draw in 90 minutes of the four-team tournament.
Lawrence Corbin-Ong had opened the scoring for the visitors after 31 minutes and defender Pansa Hemviboon equalised for Thailand in the dying moments at Chiang Mai's 700th Anniversary Stadium.
Malaysia will now face Tajikistan in the final on Sunday after Thailand meet Trinidad and Tobago in the third-place play-off.
"I have to apologise to all Thai fans for failing to help the Thai team reach the final of the King's Cup," said Polking, who vowed to steer the War Elephants to third place.
He added: "Every player did his best. I was the one who selected the players so I have to take full responsibility.
"The result in 90 minutes was acceptable because each team played well in one half. In the first half, Malaysia did better but in the second half, we made changes to our team and tactics and we played better.
"Had we played well the entire game like we did in the second half, the result would not have been like this."
Asked about the third-place play-off game against Trinidad and Tobago, the Brazilian said: "We will keep fighting. We try to do our best in every game. Although this is not the final, we are looking forward to the match. We will try to finish third."
Thailand suffered a blow after 14 minutes when playmaker and captain Chanathip Songkrasin got injured and was substituted.
The Japan-based star also offered apologies for his failure to help the team.
"I have to say sorry because I looked selfish for being able to play for only a short period. I'd like to apologise to Madam Pang [team manager Nualphan Lamsam], the coach and the fans," said the Kawasaki Frontale player.
Pansa said: "We are very disappointed that we could not meet our target. We wanted to win the trophy but missed the target.
"For the game against Trinidad, it will be tough for us. But we have to forget the defeat and keep working hard to win the next game."
Polking, 46, became Thailand's national hero when he guided the War Elephants to the Southeast Asian title in January in his first assignment as coach of Thailand.
However, Thailand have since put in unconvincing results.
Meanwhile, Australia coach Graham Arnold insisted Guus Hiddink's stint as his assistant during the 1-0 win over New Zealand in Brisbane on Thursday was a one-off and the Dutchman will not be working alongside him at the World Cup finals in Qatar.
Hiddink, an icon in Australia after qualifying the nation for the World Cup in 2006 to break a 32-year finals absence, sat on the bench for the victory in the Socceroos' final game in front of their own fans before the 2022 finals.
The 75-year-old former Netherlands and Real Madrid coach filled in for regular assistant Rene Meulensteen as part of centenary celebrations for Australia's first international and Arnold stressed that would be the limit of his involvement.
"It's for the 100-year celebration, that's all," he said.
"He's made a big sacrifice to come out. My assistant's watching France and Denmark now and Guus has come out to help with the 100-year celebration. He wanted to be part of it and that's it."