A lack of cutting edge from both teams was a feature of a match in which Lindemann had the first real chance of the game when his low diagonal shot crept wide of the post.
Tatree also had a chance when he stabbed wide, while the away sides best effort of the first half came when Farid hit a speculative overhead kick which was tipped over by keeper Todsaporn.
At the beginning of the second period, Chainarong's shot trickled wide before Ratchaburi sub Douglas had a header that went close
In the 66th minute, the deadlock was finally broken when a Bjorn Lindemann corner was nodded in by Chaiwat to give the Army the lead.
Ratchaburi never really threatened to fightback, and Chainarong really should have doubled the lead on full time after a Laurie Cunningham style dribble, but he kept the ball too long before his shot was easily blocked by Ukrit.
Man of the Match: Chaiwat Nakiem - Winning goal and clean sheet