Johnson finished with 7-of-14 shooting from the field including three from distance for the Cougars (8-1). Damyean Dotson added 16 points and six rebounds and Galen Robinson Jr. had 11 points and five rebounds.
Johnson hit four free throws and Robinson sank a 3-pointer to help bring Houston from a two-point deficit with 2:40 left in the first half to a 41-37 lead at the break.
The Cougars never trailed again. Johnson sank a pair of treys and a layup as part of a 13-9 surge early in the second half that extended Houston's lead to 60-52 with 10:52 to play. Later, he stretched the Cougars lead to 77-60 on a pair of free throws with 4:29 left and the team cruised from there.
Cornell Johnston scored 19 points for the Panthers (2-7).