The Mountaineers (16-13, 8-8 Big 12) led only 39-36 at halftime, but went on a 25-4 run starting early in the second and pulled away to a 69-44 lead on Juwan Staten's layup with 6:49 left in the game.
The Big 12's second leading scorer at 18.1 points per game, Staten had 17 points, five assists and four rebounds to join Harris, who entered the game third in the Big 12 with 18 ppg.
The Mountaineers swept the Horned Frogs (9-19, 0-16) in two games this season. They have yet to lose to TCU in four games.
Karviar Shepherd led the Frogs with 14 points, Jarvis Ray scored 13 and Kyan Anderson 10.
WVU had lost three straight coming in, but remain hopeful of finishing in the top six of the Big 12 so they can receive a bye in the first round of the Big 12 Tournament, scheduled for March 12-15 in Kansas City. The Mountaineers entered and finished the day alone in sixth place.
In the three consecutive losses for Bob Huggins' team - all by double figures - the Mountaineers shot the ball at 40 percent or worse, while allowing their opposition to shoot over 50 percent.
This day, WVU shot 43 percent (27 of 63) and held TCU to 39.2 percent from the floor (20 of 51).