Isaac Sopoaga may be the most important player on the 49ers' defense in terms of stopping the run.
If Sopoaga cannot consistently command double teams and occupy two linemen so that Patrick Willis and NaVorro Bowman can run free without a 325-pound behemoth bearing down on them, this vaunted run defense suddenly becomes a little more mortal.
So far this season Sopoaga has been a non-factor. To be fair, he played less than 20 snaps combined in Weeks 1 and 2, since he is the first off the field when the 49ers go into their nickel and dime packages, something they were forced to do early and often against Green Bay and Detroit.
But on Sunday Sopoaga figured to be in on a majority of the snaps against a team that loves to run the ball right up the middle behind center John Sullivan. It was a matchup that the 49ers needed to win if they expected to bottle up a healthy and rejuvenated Adrian Peterson.
Unfortunately, Sopoaga wasn't up to the challenge. He failed to get consistent penetration, and the Vikings guards were able to get to the second level unmolested on several occasions. Peterson and the Vikings' offensive line physically dominated the 49ers defense and Sopoaga was largely to blame.
It's not time to press the panic button on the 49ers run defense by any means. Adrian Peterson, when healthy, is the best running back in the game. And right now he looks very healthy.
However, if the 49ers want to continue forcing teams into a one-dimensional offensive attack Sopoaga will need to at least hold his own against some of the better offensive lines he'll be lining up against this season.
Much of the success of any 3-4 defense rests largely on the play of the big guy plugging up the middle.
Sopoaga played a little too small on Sunday.