49ers position roles prior to Rams game

SANTA CLARA – Here are the top things we’re learning Wednesday at 49ers headquarters ahead of this Sunday’s home game against the undefeated Los Angeles Rams:

One of the big surprises Monday night – before the stunning finish in a 33-30 defeat at Green Bay – was Raheem Mostert replacing Alfred Morris as the No. 2 running back and churning out a careerbest game. Coach Kyle Shanahan wouldn’t commit Wednesday to Mostert remaining Matt Breida’s top backup, although he didn’t rule it out heading into Sunday’s game.

“I don’t think it was a permanent change. It was what we thought was best for that game,” Shanahan said.

Mostert excelled last week in practice while Breida sat out with a sprained ankle, and, in the process, answered Shanahan’s plea to seize the opportunity and improve ball security. Mostert lost a fumble on his first carry after Breida’s injury the previous game, a 28-18 loss to Arizona

“(Shanahan) talked to me, ‘Raheem I’m going to need you to step up, focus more on ball control. I know you don’t get many reps in practice, but when you do, you have to make them count,’ ” Mostert rehashed. “That’s one thing I focused on, making my reps fully count no matter how many I got, and to control the ball.

“He knew I can be a better back than what I displayed against Arizona.”

Mostert responded with 12 carries for 87 yards, and Shanahan was convinced to play him more San Francisco 49ers’ Raheem Mostert runs with the ball against the Dallas Cowboys in the first quarter of their preseason NFL game at Levi’s Stadium in Santa Clara on Aug. 9.