Van Pelt was impressive in his first two games of the season but struggled on Saturday before leading the Rams to a late touchdown. He ran for 27 yards of his 57 yards on an 80-yard drive as Colorado State tried to avoid its first loss.
The Rams pulled within 21-19 on Van Pelt's six-yard run with 1:32 left. Van Pelt tried to run for the game-tying conversion but found little room and tried to pitch the ball to running back Cecil Sapp as he was hit by multiple defenders.
Van Pelt's throw missed Sapp and the ball was picked up by Bruins safety Ben Emmanuel, who returned the fumble for two points. The fumble capped a tough day for Van Pelt, who completed just 13-of-30 passes for 91 yards.
UCLA tight end Mike Seidman recovered the onside kick and Manuel White scored on a 15-yard run as the Bruins sealed their fifth straight season-opening victory.
Akili Harris ran for 94 yards on 13 carries and gave UCLA (1-0) the lead for good with a one-yard touchdown run with nine minutes remaining.
Sapp rushed for 105 yards on 23 carries as Colorado State (2-1)
failed in an attempt to open a season with three straight wins
for the first time since 1994.