One man's prediction: So who are the 2015 Vikings going to be after this Jekyll-and-Hyde start to the season? They are probably somewhere between what we saw in Week 1 and Week 2. This Week 3 matchup will serve as a measuring stick. The Chargers are a formidable foe, with a quality QB, a dangerous running game and a defense that could present matchup problems. I'm picking the Chargers, but this one could go either way.

Three keys

Peterson's biggest day

The last time the Chargers came to town, way back in 2007, then-rookie Adrian Peterson set an NFL single-game record with 296 rushing yards. He probably isn't going to come close to matching that mark Sunday, but he could be in for a big afternoon. The Chargers defense has allowed 4.7 yards per carry this season, and Peterson appears to be rounding into form after rushing for 134 yards on 29 carries in last week's 26-16 win over the Detroit Lions.

Hey, where's Greenway?

Vikings outside linebacker Chad Greenway played a career-low 14 snaps last Sunday. Why? The Lions relied on a three-receiver attack and Greenway is no longer an every-down player, so rookie Eric Kendricks replaced the veteran when the Vikings used their nickel package. The Chargers go three-wide even more often than the Lions, so Greenway and middle linebacker Gerald Hodges could do a lot of watching from the sideline again today.

Two kids from Kenosha

Trae Waynes and Melvin Gordon grew up together in Kenosha, Wis., and were selected four picks apart in the first round of this year's draft. Despite playing their college ball for rival Big Ten teams, they never actually lined up against each other in college. And they might not Sunday. Gordon is San Diego's starting running back, but Waynes has yet to play a defensive snap as Minnesota's fourth corner.

Player to watch

Philip Rivers, Chargers quarterback

Coach Mike Zimmer made headlines on the QB-loving NFL blog circuit when he said that San Diego's Philip Rivers was one of the best quarterbacks in NFL history. Some dismissed it as Zimmer pumping up his opponent, but he isn't one to say something he doesn't mean. Rivers, who is fourth in the NFL in passing yards, is an accurate passer but also a tough, fiery player. It makes sense that Zimmer would be a fan.

San Diego Chargers quarterback Philip Rivers (17) looks to throw a pass during an NFL football game against the Cincinnati Bengals in Cincinnati, Sunday, Sept. 20, 2015. (Jeff Haynes/AP Images for Panini) ORG XMIT: MIN2015092516073984 (The Minnesota Star Tribune)