O'Gwynne, who scored the game's only points with his second-quarter touchdown, had 13 rushing yards.
Mack's second-quarter touchdown gave Cleveland a 14-3 lead with 4 minutes 7 seconds left in the half.
Dalton Hilliard got a second-quarter touchdown on a 3-yard run.
Penn seized a 21-0 lead in the first half on three second-quarter touchdowns.
Neither did the Cowboys' inability to score a second-quarter touchdown despite two good opportunities.
Alabama extended their lead to 24-10 at halftime with a pair of second-quarter touchdowns.
Georgia then extended their lead to 37-10 by halftime with four second-quarter touchdowns.
The teams traded first-quarter field goals and then second-quarter touchdowns.
The Knights scored three second-quarter touchdowns, two of them generated by the defense.
Green ran 2 yards for a second-quarter touchdown and 1 yard for a score in the third period.