The Panthers (24-5) will play Westbrook Christian in Saturday's 10:40 a.m. final. Westbrook Christian beat LaFayette 49-48 earlier in the day.
Fyffe finishes 24-8.
Orendaz Holloway added 16 points and Marlon Bridge Jr. 11 as 10 Lanett players scored. Austin Stiefel led Fyffe with 13 points, and Trenton Thrash scored 11.
The game was all but decided in the second quarter, after Fyffe went on a 10-1 spurt to climb within 19-18 on Stiefel's 3-pointer at 6:39. Lanett answered with a 19-2 run to take a 38-20 lead on Bridge's jumper at 2:07.
Lanett outscored Fyffe 42-14 in the paint, 27-6 on second-chance points and 28-12 off turnovers.