SMU's secondary couldn't stop Tech's passing attack, even though the Red Raiders (1-0) were without Jarrett Hicks, one of their leading receivers who is awaiting word from the NCAA on an appeal of his academic eligibility.
Harrell's favorite target was Robert Johnson, a quarterback turned receiver who caught two touchdowns and finished with 139 yards on 15 catches. His showing broke a Tech record for most receptions in a game set in 2002 by Wes Welker (14) in the Red Raiders 42-38 win over then-No. 3 Texas.
The five touchdown passes by Harrell, who holds the Texas high school record for touchdown passes in a season with 67, bested first-outing performances by his four predecessors. Cody Hodges had four TD in his debut last year, as did Sonny Cumbie the year before. B.J. Symons had three and Kliff Kingsbury threw two.
Harrell's 45-yard scoring pass went to Danny Amendola late in the third quarter to put Tech up 28-3.
Harrell, who completed 34-of-49 passes, showed poise even as the Mustangs pressured him with numerous blitzes. Though he ran a couple of times, he seemed more comfortable hanging in the pocket until he found an open receiver.
SMU (0-1) jumped in front with a field goal and had a good opportunity to pull within 11 points early in the second half. Blake Warren nearly returned a punt for a touchdown but was tackled by Tech punter Alex Reyes at the Red Raiders' 26.
Four plays later, after first-time starting quarterback Justin Willis fumbled the snap and lost 9 yards, the Mustangs missed a field goal from 49 yards to trail 21-3.
SMU finished last season on a three-game win streak, but the Mustangs faded as the game wore on. They got only 64 total yards and four first downs in the second half. Tech held SMU to 189 total yards.
Tech unveiled its new FieldTurf surface to fans. Gone is the tired AstroTurf -- Tech was one of the last schools in the country with the surface -- and the crown over the center of the field that aided in drainage. Also missing was the running track that used to encircle the field.
The school also built a low, brick wall around the perimeter of the field area to match the facade on the stadium's west side.