Texas lost starting quarterback Quinn Ewers in the second quarter of Saturday's game against UTSA at Darrell K. Royal-Texas Memorial Stadium in Austin.
But reserve Arch Manning and the Longhorns never trailed.
With Texas leading 14-0, Manning led a four-play, 72-yard drive that culminated in a 19-yard touchdown pass to DeAndre Moore Jr. to give the Longhorns a commanding 21-0 lead.
UTSA scored a touchdown on their next possession to cut the lead to 21-7, but Manning's offense wasn't done.
On the next drive, Manning, Cooper's son and Peyton and Eli's nephew, went 75 yards in just two plays to lead Texas to the end zone.
On the second play of the drive, Manning scored a 67-yard touchdown run to give Texas a 28-7 lead, which they held until halftime.
In a halftime interview with ESPN, Texas coach Steve Sarkisian said Ewers, a Heisman Trophy candidate, suffered an abdominal strain.
Ewers was injured while handing the ball off to running back Quintrevion Wisner, who limped away, collapsed and called for a trainer.
Ewers spent about 15 minutes in the medical tent before heading to the locker room under his own steam midway through the second quarter.
Ewers, who will not return, returned to the Longhorns sideline in street clothes late in the second quarter and was holding his ribs while talking to trainers.
