Riley Payne scored 22 points, 12 in the fourth quarter, sending Idalou to the Class 2A state championship with a 55-54 win over Tatum on Saturday.
Payne made one of two free throws with 17 seconds left to put Idalou ahead by three.
Tatum had a last chance to force overtime but Neil Harkless' 3-pointer with 1 second left missed everything, leaving Desmond Fite to drop in a layup at the buzzer for the final points.
Payne was 10 of 15 shooting from the field. Luke Bucker had 10 points and 12 rebounds and Bradley Adkins scored 10 for Idalou (33-1).
Fite finished with 21 points, Kendall Bell scored 16 and Dylan Starling scored 11 for Tatum (32-8).
Brandon Woodard, who made five 3-pointers for Tatum in a semifinal victory, did not play.
Without him, Tatum was 4 of 28 shooting from long range.
Kainon Irons had 31 points and 14 rebounds and Clyde Eula beat Tenaha 64-49 Saturday to win the Class 1A Division I state championship.
Irons, who scored 32 of Eula's 54 points in the semifinals against Evadale, was just four points shy of the 1A championship game record of 35, set by Calvin Gerke of Snook in 1966.
Jacob Archa had 16 points and 13 rebounds and George Reyes added eight points for the Pirates (37-2).
Reginald Davis had 20 points and 14 rebounds for Tenaha (28-10).
Clyde Eula led 42-37 to start the fourth quarter. A 3-pointer by Archa stretched the lead to eight and Irons scored eight points in the final period as Clyde Eula pulled away.