FORT WORTH, Texas -- No. 20 TCU found itself in a dogfight and in position to go into halftime trailing on its home field.

That all changed in three seconds.

Kenny Hill's surprisingly easy 38-yard Hail Mary touchdown to Jalen Reagor to close out the first half gave the Horned Frogs the push they needed and a lead they wouldn't relinquish.

"It made a huge difference, it gave us a little something going into halftime and deflated their momentum," Hill said. "That's the first time I've ever been in a game and seen a Hail Mary completed. Reagor was on this sideline saying, 'Throw it up there and let me make a play,' so that's what I did."

Hill threw for four touchdowns as TCU stormed back to thrash longtime rival SMU 56-36 at Amon G. Carter Stadium on Saturday afternoon.

The Horned Frogs (3-0) rallied from an early 12-point deficit with a flurry largely piloted by Hill.

Hill picked apart the SMU secondary with a series of quick and accurate throws that ate up yardage. The senior completed an efficient 24 of 30 passes for 365 yards and did not throw a pick.

TCU running backs Darius Anderson and Kyle Hicks combined for 173 yards rushing. Anderson scored twice and helped put the game away with a 38-yard score in the fourth quarter. Reserve running back Kenedy Snell also had two touchdowns.

The Horned Frogs finished with a 619-463 edge in yardage.

TCU, with a dominating win at Arkansas last week, completed nonconference play looking every bit the part of a Big 12 title contender. The Frogs will see if they really are next week, as they travel to No. 9 Oklahoma State.

"The second good test is going to be on the road in Stillwater," TCU coach Gary Patterson said.

The Mustangs (2-1) have been dominated in the series in the Patterson era but had to feel better in their third year under coach Chad Morris. SMU started 2-0 for the first time since 2009 and scored more than 50 points in each of the first two games.

But the Mustangs lost to TCU for the sixth straight year, the last three under Morris.

"There is no doubt that our football team has gotten better and continues to get better over our third time playing them," he said. "I'm pleased where our program is heading. Obviously, we'd love to get the win tonight, but when you play an opponent like TCU and what they've built here, it comes down to four or five plays."

SMU quarterback Ben Hicks did his best to keep the underdog Mustangs close. Scrambling to buy time and not afraid to take shots deep down the field, the sophomore threw for 305 yards on 17 of 37 attempts. Hicks threw two interceptions, the first returned for a touchdown in the fourth.

Hicks' favorite target, junior receiver Courtland Sutton, was held in check. Coming off a four-touchdown game against North Texas, Sutton was limited to one catch on seven targets.

Mustangs running back Ke'Mon Freeman had two touchdowns, including a 34-yard score late in the third that pulled the visitors within 35-29.

The Horned Frogs were able to overcome two lost fumbles, both coming deep in their territory. SMU was only able to convert those turnovers into one field goal.

The Mustangs went up 19-7 thanks to a pair of long touchdown drives, along with two field goals set up by a fumble recovery and missed field goal.

TCU struck back to take a 21-19 lead on two Hill touchdown passes, the latter a 71-yard catch-and-sprint by Snell.

Hicks engineered another long drive that ended with a short field goal for a 22-21 lead with 17 seconds before halftime, but that was enough time for Hill and Co.

A decent kickoff return and long run by Snell carried the Frogs to the SMU 38 with three seconds remaining. Hill's heave into the end zone was easily pulled in by a leaping Reagor with no resistance from a host of Mustangs defenders, and TCU went into the locker room leading 28-22.

"We knew they were going to throw it," Morris said. "Three seconds, that's what you do. We practice it. We put our guys in position. They had one guy jump. We had nobody jump."

NOTES: TCU leads series 50-40-7. ... SMU finishes its nonconference schedule next week with a home game against Arkansas State. ... The Horned Frogs are 3-0 for the ninth time in 17 seasons under coach Gary Patterson. ... SMU WR Courtland Sutton had a streak of games with a receiving touchdown snapped at five.