49ers’ breakout back: Will sixth-round rookie Mitchell get starting shot?

LEWISBURG, W.VA. — Rookie Elijah Mitchell is on pace for a 1,768-yard rushing season.

What's actually fair to expect, however, from a sixthround rookie who completed the 49ers' draft class?

Mitchell, history says, will get a chance to parlay his 104yard debut into a consistent role as the 49ers' starting running back.

That job opened up early in Sunday's 41-33 win at Detroit, once Raheem Mostert bowed out with torn knee cartilage that will require surgery and sideline him for the season, Mostert announced Tuesday.

Here are a couple of reasons Mitchell was Mostert's immediate replacement, which caught many off guard:

1. Trey Sermon was drafted much higher (third round) and played big-time college football at Ohio State and Oklahoma (all due respect to Mitchell's time at Louisiana).

2. Mitchell missed the first two preseason games with a core muscle injury.

Mitchell won over the 49ers' brass the past couple weeks, however.

“History shows you can get them in the first round, you can get them in the sixth round, and you can get them undrafted,” coach Kyle Shanahan said of running backs.

“There are always some diamonds in the rough that you can look for,” Shanahan added. “And by no means do we hit on every one.”

Sunday's encore at Philadelphia likely will keep Mitchell as the 49ers' mainstay, with Sermon making his delayed debut in a relief role alongside Jamycal Hasty.

If those three young rushers struggle or get injured, Jeff Wilson Jr. should be available for the season's second half, if his knee recovery cooperates.

Mitchell said position coach Bobby Turner informed him a couple of days before his debut he'd be RB2 against the Lions. Sermon was a healthy scratch.

“Coach Bobby T. coaches everybody the same and keeps us ready to go because things hap