TCU was able to hang with No. 17 San Diego State for several minutes Saturday night, even taking a 23-16 lead thanks to five 3-point shots.
Then it started to go sideways for the Horned Frogs, who quickly gave up the lead and lost 83-73.
Jamaal Franklin had 24 points and 11 rebounds for the Aztecs, who clinched their seventh straight 20-win season.
James Rahon added 16, Chase Tapley 14 and DeShawn Stephens 13 for the Aztecs (20-3, 6-1 Mountain West). SDSU has eight 20-win seasons overall in 13 seasons under coach Steve Fisher, including last year's school-record 34-3 performance.
With No. 11 UNLV losing at Wyoming, the Aztecs regained sole possession of the conference lead.
Kyan Anderson had 22 points and J.R. Cadot 15 for TCU (13-9, 3-4), which lost its seventh straight to SDSU.
Coach Jim Christian said the Horned Frogs were undisciplined.
"There's not one thing. It's a bunch of things," he said. "It's disciplined stuff. We're just not being consistent and disciplined, especially on the defensive end of the floor. You're not going to be able to beat them."
Said guard Hank Thorns: "We just did not play a very good game. We had too many mistakes and it's hard to beat a good team like San Diego State when you play like that. It's hard to know how to fix it. We were trying tonight, but nothing seemed to work."
After shooting just 31.3 percent from the field in a 17-point loss at Colorado State and a two-point home win against Boise State, the Aztecs made 50.8 percent of their shots. Several nice dunks helped the Aztecs with the better percentage, including one when Franklin came flying in for a rebound and an impressive reverse slam that made it 39-31 in the first half.
SDSU outrebounded TCU 35-21.
"It did feel like we were back to normal," Franklin said. "We were actually running the ball and we weren't really relying on set plays. We just ran the ball, everyone contributed and we got open shots."
San Diego State overcame an early deficit to take a 46-39 halftime lead, and then outscored the Horned Frogs 12-6 to start the second half. Franklin hit a bank shot and Tapley had a layup and two free throws to open the half. Franklin hit a jumper, Tapley had another layup and Garrett Green a reverse slam dunk to push the lead to 58-45 with 16:10 left.
TCU made four 3-point shots in the first 7:15 to take a 23-16 lead.
The Aztecs tightened their defense and went on a 17-4 run to jump ahead 33-27 with 4:46 before halftime. Franklin started the run with a dunk and Rahon added a 3-pointer.
Stephens had three points during the run and had six more the rest of the half, including consecutive baskets for a 37-29 lead.