Lampang and Nongbua Pitchaya have punched their tickets to Thai League 2 after sustaining losses in the top flight on Sunday night.
Bottom club Lampang suffered a 3-1 home loss to Chonburi and Nongbua were beaten by the same scoreline at Muang Thong United.
Lampang have 16 points, one less than Nongbua's tally.
With three games remaining, the fight to avoid the last relegation spot could be fierce.
Lamphun are on 27 points, two behind Prachuap, Nakhon Ratchasima and Khon Kaen.
Adul Lasoh got off to a winning start as coach of Chonburi who comfortably beat Lampang 3-1 with goals from Danilo Alves (24), Yoo Byung-Soo (85) and Saharat Sontisawat (87).
At Thunder Dome Stadium, Brazilian forward Willian Popp scored twice as hosts Muang Thong condemned Nongbua to Thai League 2.
Willian opened the scoring after 11 minutes only for Barros Tardeli to equalise just before half-time.
Willian was on target again in the 68th minute and Weerathep Pomphan made it 3-1 in injury time.
The Kirins moved up to third -- the last AFC Champions League spot.