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The rebuilding Vikings have their work cut out for them against the powerful San Francisco 49ers.

Here are four things that need to go right for the Vikings (1-1) if they're to experience another "Metrodome Miracle" against the 49ers (2-0), On Sept. 27, 2009, Brett Favre threw a 32-yard touchdown pass to Greg Lewis in the back of the end zone with two seconds left to pull out a 27-24 win.

  • Allen gets off the schnide: It must be some kind of record whereby the previous season’s sack leader -- DE Jared Allen with 22 -- gets shut out of sacks in the first two games the following season. But that is the case for Allen, and if it happens for a third game against the 49ers, someone will probably look it up. Allen will be working hard to erase that goose egg against Niners QB Alex smith, who has been sacked 51 times since the beginning of the 2011 season, the most in the NFL over that period. Allen also would like to erase the memory of last week’s roughing penalty of Colts QB Andrew Luck. A couple sacks that lead to a win would help.
  • Reduction in penalties: The Vikings committed 11 penalties for 105 yards in last week's loss to the Colts, who had 278 yards of offense. Clearly, penalties led to the Vikings' loss of a winnable game. Against the 49ers, they don’t have the luxury of making that many mistakes and still being close at the end of the game like they were against the Colts. The Vikings must play mistake-free football, both in the penalty and turnover categories, because the 49ers will take full advantage of every mistake they make.
  • Linebackers in pass coverage: This aspect of the Vikings defense was already suspect before WLB Erin Henderson suffered a concussion and sidelining him for Sunday's game. With 49ers TE Vernon Davis coming to town, the Vikings linebackers will be on full alert. Smith is tied for the most touchdowns in the league (3) and QB Alex Smith will surely be looking for him when Vikings LB Jasper Brinkley, who previously came off the field during nickel situations, drops into coverage.
  • Pick your poison -- Peterson or Harvin: RB Adrian Peterson has to rip off longer runs than he did last week, when his longest one was six yards. If the 49ers load the box, it should open up the field for WR Percy Harvin. If the 49ers double Harvin, then it's up to Peterson to gain yards on the ground. The 49ers defense could likely do both and shut down the Vikings offense unless someone else such as TEs Kyle Rudolph and John Carlson or a wideout steps up as a credible threat.

For more Vikings news and notes, follow Joe Oberle on Twitter @CBSVikings.