You'd think if you had the best running back in football, you'd figure out a way to hold on to halftime leads of 10, 17 and 20 points and go 3-0, right?

But that hasn't happened because the Vikings haven't come anywhere near achieving their goal of controlling the game with a heavy dose of Adrian Peterson and a veteran game manager in Donovan McNabb at quarterback.

Peterson has been shut down in the second half, while McNabb has been able to post only two field goals in 16 second-half possessions. McNabb is 1 for 11 passing with no conversions on third down in the second half. As a team, the Vikings are 1 for 15 on third downs in the second half, and that includes a current 0-for-14 skid since the 10-minute mark of the third quarter in San Diego.

That's 85 minutes of game clock in which the Vikings have not converted a third down or a fourth down (one).

Meanwhile, Peterson has been taken out of games that you'd think he would be able to finish off. He had 12 carries for 73 yards in the first half of Sunday's 26-23 overtime loss to the Lions. He had five carries for 5 yards in the second half.

For the season, Peterson has 230 yards and three TDs on 29 first-half carries (7.9). In the second half, he has 66 yards and no touchdowns on 22 carries (3.0).

So while the defense is far from innocent with 67 points and 698 yards passing -- including 314 by Matthew Stafford -- in the second half, it's the offense that is the main culprit in what's quickly becoming (or has already become) a lost season.