The season's first week did nothing to quiet the critics who felt Peyton Manning's age and Adrian Peterson's layoff would hinder their performances in 2015.

They're likely feeling much differently now.

Manning looks to help guide the Broncos to their second 4-0 start in three years while Denver's top-ranked defense tries to slow Peterson and the visiting Minnesota Vikings on Sunday.

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The 39-year-old Manning failed to throw a touchdown pass in his second consecutive regular-season game and also tossed an interception in the Broncos' 19-13 home win over Baltimore on Sept. 13.

He bounced back with three TD passes to help rally Denver from 14 points down to beat Kansas City the following week, then went 31 of 42 for 324 yards and two scores Sunday night in a 24-12 victory at Detroit.

None of the wins came easily, and Manning even quipped Wednesday with a reporter who indirectly suggested he made only a few good throws against the Lions.

"If we can keep improving and win games at the same time, that's a real positive," Manning said. "Offensively we want to be able to do our part. We know our defense is playing at a high level, but we'll have our hands full against (the Vikings) on Sunday."

Denver's defense is allowing the league's fewest yards per game at 259.0 and has forced the second-most turnovers with 10. It ranks eighth in opponents' yards per carry at 3.54, considerably less than Peterson's 4.93 average.

Peterson missed the final 15 games last season after being suspended by the league for a child abuse incident involving his son, but that didn't stop him from suggesting he would return to form in 2015 despite the time away.

He ran only 10 times for 31 yards in a season-opening loss at San Francisco, then finished with 134 yards in a win over Detroit on Sept. 20 and rushed for 126 and two touchdowns in last week's 31-14 victory over San Diego.

Peterson again didn't shy away Wednesday from boasting that he's the NFL's top back despite being 30.

''Who is a better running back than me?'' Peterson said, pausing for nearly a minute. ''Peyton Manning's got some nice moves."

Vikings coach Mike Zimmer spoke more seriously about Manning's abilities having faced him as a defensive coordinator in other stops around the league.

"He still looks like Peyton Manning to me," Zimmer said. "He's extremely accurate, he gets the ball out quick and he sees a lot of things. There's probably not a blitz we can devise that he has not seen and there's probably not a coverage that we run that he has not seen. If you make a mistake, he's going to find it."

It's a level second-year Minnesota quarterback Teddy Bridgewater aspires to reach, but he might not have much time to think in the pocket this week. The Broncos are allowing an NFL-low 176.3 yards through the air, and their 11 sacks are tied for second.

DeMarcus Ware has 3 1/2 and forms part of a dangerous pass-rushing duo with linebacker Von Miller.

"We know that defense is playing some great football right now and everything starts up front with those guys," said Bridgewater, who has completed 67.6 of his passes but has only one touchdown and two picks. "We know that defense runs through those guys and they play with a ton of confidence. We're just going to approach this game with the mindset that we have to be physical and play fast."

The Vikings' defense got some good news Wednesday when cornerback Xavier Rhodes passed post-concussion tests and returned to practice after colliding with safety Andrew Sendejo trying to make a tackle last week. Rhodes is expected to play in this contest.

Denver left tackle Ty Sambrailo didn't practice Wednesday because of a shoulder injury and is considered day to day. He suffered the injury blocking for C.J. Anderson last week but remained in the game.

Anderson and the rest of the Broncos' running game rank last in the league at 2.59 yards per carry, but Minnesota is allowing 4.31 yards per rush to rank 25th.