Mostert racked up 57 yards on just eight carries in Thursday's preseason win over the Cowboys. He also lost a fumble.
Mostert outperformed Joe Williams in terms of yards gained in the two backs' ongoing competition for a third-string role. He did lose a fumble in the third quarter, however, as the 49ers inched close to the red zone. Projected No. 2 back Matt Breida exited the contest with a shoulder injury, so the winner of this job battle could be in line for a larger role than initially expected depending on the length of Breida's absence. Mostert will need to quickly put the turnover behind him if he's to stake his claim to a role in the offense when the regular season rolls around.