"Neither was the Texas defense, it was their worst performance of the year. Yet they still won."
I think they were cramping from the heat, but I am not sure.
Both defenses played very hard, but I think Texas was worn out earlier due to having fumbled the first kick off from USC in the first quarter.
Texas had cramping problems throughout the game. Possibly, I'm guessing, flu or cold related, possibly also the heat of the night game. Colder at night in Texas, and their bodies diurnal cycle had acclimated to the Texas daily temparature cycle.