The Aztecs (6-3, 5-0 Mountain West) reached 5-0 in conference for the first time since becoming a Division I team in 1969.
Colorado State (3-5, 1-3) stayed close, trailing 13-10 at the break. San Diego State scored four touchdowns after halftime, including a 55-yard interception return by Damontae Kazee for his first career touchdown.
Pumphrey rushed for 121 yards on 20 carries, breaking 100 yards for the fifth straight game, and surpassing 1,000 yards for the season. He scored from the 1 in the first quarter, and added a 64-yard run in the final quarter.