FORT WORTH, Texas (AP) -- TCU's offense needed a much overdue spark to get things going.
Once it finally came, the Horned Frogs couldn't be stopped.
TCU's defense forced five turnovers, and quarterback Trevone Boykin led five straight second-half scoring drives to help the Frogs overcome a halftime deficit and rout rival SMU 48-17 on Saturday.
Boykin completed 15 of 26 passes for 228 yards and two touchdowns, but he had to overcome a sluggish start before TCU had a 31-point fourth quarter in its highest-scoring output of the season.
He erased boos and a 7-of-16 first-half performance by completing seven of his first nine passes in the second half, tossing touchdown passes of 20 and 56 yards to help the Horned Frogs (2-2), who trailed 10-7 at the half.
''It was like we played with more emotion,'' Boykin said. ''We were pretty flat and just trying to make some plays with our athletic ability and things weren't going right for us. We were killing ourselves with offsides and personal fouls, but we made some good halftime adjustments and tried to stick to our game plan as well as possible and we came out with the win.''
TCU retains the Iron Skillet trophy for the second straight year, and they are 11-2 under coach Gary Patterson in the annual rivalry game.
''I got after the offense pretty good at halftime,'' Patterson said. ''They've got to start understanding at some point in time that they have to look at themselves. They did a better job in the second half.''
SMU (1-3) had only 292 total yards. Garrett Gilbert completed 23 of 44 passes for 276 yards and four interceptions, and TCU also had had seven sacks - its most since eight at Virginia four years ago.
''Our defense played a heck of a game today,'' Gilbert said. ''Offensively that's completely on us. We didn't keep them off the field by sustaining drives in the second half. Felt great about the first half, played well, thought we had some stuff to build on.''
TCU played without star defensive lineman Devonte Fields, who was out with an unspecified injury.
Without Fields, the 2012 Big 12 defensive player of the year as a freshman last season, the TCU defense struggled to get much rush on Gilbert early on, but it bottled up the middle of the field. SMU's running backs combined for just 18 yards on 10 carries in the first half.
TCU's defense stepped up in the second half, forcing six straight incompletions from the former Texas starter and picking up the pass rush. After TCU tied the game at 10 on a 35-yard field goal by Jaden Oberkrom, Gilbert was intercepted by Sam Carter and returned 25 yards to the SMU 32.
After driving inside the 10 following the interception, the snap went through the legs of Boykin to set up a third-and-18 from the 20, but the sophomore quarterback found Ty Slanina in the left corner of the end zone to put the Frogs up for good.
''It wasn't pretty early,'' Patterson said. ''They've caused people problems on defense. Again, you can't have penalties. We get down, we turn the ball over and have personal fouls, jump offsides. We did what we needed to do.''
Boykin led five straight scoring drives in the second half, which included a 6-yard touchdown run by B.J. Catalon with 10:33 left in the fourth quarter to give TCU 31-10 lead.
After SMU cut the lead to 35-17 with 3 minutes left in the game, LaDarius Brown returned an onside kick 45 yards for a touchdown, and Carter returned his second interception of the game 66 yards for another score.
The Frogs, playing for the first time in 16 days after losing their Big 12 opener at Texas Tech, went four possessions without a first down in the second quarter. That included a missed 42-yard field goal after an SMU fumble in its own territory.
TCU also stalled at its own 10 late in the second quarter, and Ethan Perry's punt was deflected by Jackson Mitchell close to the end zone. The ball sailed to the 11 and was picked up by Ajee Montes, who returned it to the 1.
Fortunately for the Frogs, SMU's offense fared no better in the opening half. After Prescott Line was dropped for a loss of 1, Gilbert fumbled a low snap and although the Mustangs recovered, SMU had to settle for a 34-yard field goal by Chase Hover with 58 seconds left in the half.
''We had a blocked punt that we didn't score and only got a field goal out of it,'' SMU coach June Jones said. ''You got to score touchdowns, but we gave them an opportunity to feel like they had some success.''
The Mustangs opened the scoring with a 1-yard touchdown pass from Gilbert to Jeremy Johnson with 4:41 left in the first quarter. Johnson led SMU with 11 catches for 159 yards.
Waymon James, who led TCU with 54 yards rushing on 11 carries, scored from 2 yards out 9 seconds into the second quarter to make it 7-7.