A last-gasp goal on Saturday gave Singhtarua a 2-1 home win against Air Force in League One, securing promotion to the Thai Premier League.
Singhtarua fans celebrate their return to the Thai Premier League.
PTT Rayong also gained promotion to the top flight after a 2-2 home draw with Bangkok FC, with Air Force winning the title.
Air Force finished the season on 69 points, Singhtarua 65, PTT Rayong 64 and Bangkok FC 62.
At PAT Stadium, former powerhouse Singhtarua (formerly Thai Port) went ahead through Leandro de Olivera's penalty after 58 minutes.
Diarra Ali equalised for Air Force in the 90th minute and Sarawut Kongcharoen scored the winner for Singhtarua deep into injury time.
Bankok United needed a win at PTT Rayong to be promoted to the top league but could manage only a 2-2 draw, which was enough to send the hosts to the TPL.
Meanwhile, Pattaya United are on the brink of relegation on the final day of the Thai Premier League season today.
The Blue Dolphins have 26 points, three less than Samut Songkhram, the other candidates in the fight to avoid the drop.
In order to stay up, Pattaya must win at Insee Police United and hope Samut Songkhram lose at home Ratchaburi. That would leave Pattaya and Samut Songkhram equal on points but allow Pattaya to remain in the top flight because of their better head-to-head record.
"It is a difficult task because we will be playing an away match," Pattaya United coach Jadet Meelarp insisted. "However, we will play our best and I will send the best squad for this match. We have to get the three points."
Insee Police coach Thawatchai Dumrong-ongtrakul insisted his side would not allow Pattaya to get an easy victory.
"Although this match is meaningless for us, we will not give Pattaya United an easy game," he said.
"We will be playing in our home ground so we have to beat them."
Samut Songkhram can ensure their survival by earning one point or better against Ratchaburi but coach Somchai Chuayboonchum acknowledged it will be hard to take the three points.
"We are the underdogs against Ratchaburi and we will be without several key players, such as Guy Hubert and Jung Ho-Jin," he said. "We also have to check the fitness of Jetsada Poolek but I am confident that the team will get at least a point."
Buriram United, who won the title last week, will be aiming to complete the season undefeated when they host TOT.
After the match, Buriram will be presented with the trophy at I-Mobile Stadium.
However, Worawi Makudi, who has been at odds with Buriram chairman Newin Chidchob, has refused to present the trophy to the Thunder Castle, saying he is no longer president of the Football Association of Thailand.
Buriram will face Bangkok Glass in the FA Cup final and take on Ratchaburi in the League Cup showdown.
(all kick-offs 6pm)
Songkhla United v Suphanburi (Tinsulanonda stadium); Buriram United v TOT SC (I-Mobile stadium); Chiang Rai United v Bangkok United (United stadium); Insee Police United v Pattaya United (Thammasat stadium); Samut Songkhram v Ratchaburi (Samut Songkhram stadium); Osotspa M-150 Saraburi v Chonburi (Saraburi stadium); BEC Tero Sasana v Army United (Chalermprakiat 72nd stadium); SCG Muang Thong United v Chainat (SCG stadium)
Buriram! 31! 22! 9 ! 0 ! 71! 21 ! 75!!
Muang Thong! 31 ! 21 ! 7 ! 3 ! 59 ! 31 ! 70!!
Chonburi ! 31! 17! 8 !6 !56 !34 !59!!
Suphanburi ! 31 ! 14 ! 9! 8! 39! 29! 51!!
Bkk Glass ! 32! 14! 8 ! 10 ! 40 ! 31 ! 50!!
Army ! 31 !13 !9! 9 !46 ! 35 !47!!
BEC ! 31! 12! 9 ! 10! 52 ! 48 ! 45!!
Osotspa ! 31 ! 9 ! 12 ! 10 ! 37 ! 39 ! 39!!
Insee Police ! 31 !9 !11 !11 !39! 35 !38!!
Chainat ! 31! 10! 7 ! 14 ! 40 ! 41 ! 37!!
Chiang Rai ! 31! 7 ! 10 ! 14 ! 28! 43 ! 31!!
Bkk Utd ! 31 !8! 7 !16! 36 !57 ! 31!!
TOT ! 31! 8 ! 7 ! 16 ! 26! 52 ! 31!!
Ratchaburi! 31 ! 6 ! 11 ! 14 ! 29 ! 37 ! 29!!
Songkhla ! 31 !6 ! 11 !14! 28 !46 ! 29!!
S Songkhram ! 31! 6 ! 11! 14 ! 20! 39 !29!!
Pattaya ! 31 !8 !2 !21 !37 !65 ! 26!!
Si Sa Ket ! 0 ! 0 ! 0 ! 0 ! 0! 0 !0!
Note: Si Sa Ket will remain in the TPL next season. Only the 17th-placed team will be relegated to League One