MINNEAPOLIS -- For every football fan who has ever started a season predicting their favorite team will "be pretty good, if they stay healthy," the 2016 versions of the Houston Texans and Minnesota Vikings stand as reasons to throw that logic out the window.

When the Vikings (4-0) host the Texans (3-1) on Sunday afternoon -- in the first day game played inside Minnesota's sparkling new U.S. Bank Stadium -- it will showcase a pair of rosters that look much different than the ones that took to the practice field a month ago. Yet both teams are atop their respective divisions after one-fourth of the season, and neither has given fans a reason to view them sympathetically.

The concept of "next man up" has been tested repeatedly in both Houston and Minnesota early on, with Texans star defender J.J. Watt out of the lineup for the season with a back injury, while the Vikings lost starting quarterback Teddy Bridgewater and star running back Adrian Peterson -- both most likely for the season -- before the end of Week 2.

An ugly 27-0 blanking of Houston by the Patriots a few Thursdays ago is the only blemish on either team's record, and both are doing it with defense. Although the Texans defense took another hit on Wednesday when the team placed defensive end Devon Still on injured reserve due to a foot injury. Brandon Dunn was elevated the from the practice squad as a replacement.

The Texans enter Sunday's visit to Minnesota -- just the second in franchise history -- leading the league in pass defense, which they hope will pose a problem for new Minnesota quarterback Sam Bradford.

While offense has hardly been the story in the Vikings hot sprint to the quarter pole, Bradford has played safe, mistake-free football in his three starts (since coming over from the Eagles in a trade on Labor Day Weekend) and has repeatedly found favorite targets like wide receiver Stefon Diggs and tight end Kyle Rudolph.

"He's one of those guys that I think we had a bond early," Bradford said of Rudolph, after the pair connected for a touchdown in the Vikings 24-10 win over the Giants on Monday night. "He was a guy that I've trusted since I've got here. He's such a big target and he's got strong hands. He makes a lot of tough contested catches. ... It's nice having targets like that."

Texans quarterback Brock Osweiler has plenty of targets, too, and he took advantage of them in Houston's 27-20 home win over the Titans last week. Osweiler connected with rookie wide receiver Will Fuller seven times in the win over Tennessee, but also connected with Titans defenders twice and has thrown six interceptions in the Texans' first four games.

That's a trend the team knows cannot continue if they hope to become the first visitors to win a game in the Vikings' new home.

"I just think overall we just need to come out with a better sense of urgency in the second half, and that's going to be a big focus for us along with many other things as it relates to Minnesota this week," Texans coach Bill O'Brien said on Monday.

Despite being the defending division champions, the Vikings were widely picked as a potential Wild Card team behind Green Bay in the NFC North -- and that was before the significant injuries happened. But Minnesota is making believers with its defense and is in the heads of opponents as one of only three remaining unbeaten teams in the league.

The Vikings' biggest concern may be in the kicking game, where Blair Walsh's confidence has been rattled, seemingly since his missed late chip shot cost the team a playoff win last winter. He has three misses in four games and pushed a 46-yard attempt wide left versus the Giants.

"I don't know. I wish I knew; I wish I knew," Minnesota coach Mike Zimmer said when asked about his confidence in Walsh. "We need to make those or it's going to bite us in the rear end."

On Tuesday Zimmer said he's not bringing in another kicker to compete for the job, at least not yet, and said Walsh's struggles were something the Vikings intend to fix and move on.

The Texans' only previous road game was that forgettable Thursday night in New England, so they know a better showing will be required in Minnesota.

"That's something that we have to answer," Houston linebacker Whitney Mercilus said. "How can we play great on the road? We haven't done that yet, so this is a great, great test for us to show everybody that we can win on the road, especially in an environment like that."

Sunday's game will be the fourth all-time meeting between the Vikings and Texans. Minnesota has won the first three, most recently by a 23-6 score in Houston in December 2012.