Chainat, already assured of a quick return to the top flight, put the icing on the cake in a bizarre fashion on Sunday night, when they claimed the Thai League 2 title at the end of an unexpected defeat.
Having already punched their ticket to Thai League 1, the Hornbills were crowned champions of the second-tier league after a 4-2 loss at Kasetsart.
Despite the defeat, Chainat are uncatchable with one match remaining.
They have 64 points and are placed ahead of Air Force Central (59) and PT Prachuab (54).
Air Force and Prachuab have also managed to earn themselves spots in next season's Thai League 1.
Chainat were relegated from the top league last season when the Football Association of Thailand cancelled the remaining games after the passing away of King Bhumibol Adulyadej in October 2016.
Chainat complained that the decision was unfair as they believed they could have avoided the drop if the remaining matches had been played.
However, they did not lodge a formal protest.
Meanwhile, the Football Association of Thailand (FAT) is keen to use the future SEA Games as a breeding ground for stars of the future.
FAT technical chairman Witthaya Laohakul yesterday told a meeting at the Sports Authority of Thailand headquarters, which was presided over by Tourism and Sports Minister Kobkarn Wattanavrangkul, that Thailand planned to send U20 players to the SEA Games.
Thailand completed a hat-trick of men's football gold medals at the multi-sport SEA Games in Malaysia in August, when the age limit for participating players was reduced to from 23 to 22.
"Using young players will pose a higher risk to our chances of winning the gold medal at the SEA Games, but it will prove beneficial for national football in the long run," Witthaya said.
He added that the planned change would apply only to the men's team, and would have no bearing on the squads for the women's and futsal competitions of the games.
The next SEA Games will be staged in the Philippines in 2019.
