On Thursday night Casey left West Virginia in a 43-40 win over Baylor.
Mathis said, "He didn't put any extra pressure on himself to perform in Donaldson's absence."
He surpassed last year's own record against Kansas.
West Virginia coach Neil Brown said, "He was decisive and that's not the place this year."
Baylor had one last chance but the backup quarterback threw two imperfections.
At the end of time, tackled a scuffle near midfield.
The Bears lost to quarterback Blake Sheppen in the third quarter after slipping at the end of a scuffle
Baylor coach Dave Aranda said, "Shapen and injured running back Craig Williams will get examined on Friday "and we should have an idea after that”.