For such a fast team, the Cardinals sure start slow. And they don’t always finish so well, either. And they’re 4-4-1 with wins over teams that have a combined record of 8-20.

But …

Coach Bruce Arians will have an ample stockpile of weapons when he arrives at U.S. Bank Stadium to face the free-falling Vikings (5-4) on Sunday. He has the No. 3 scoring defense and an offense that can throw deep to multiple speedsters, move the chains with arguably the strongest, most physical receiver of all time in Twin Cities native Larry Fitzgerald Jr., and essentially do whatever he wants to with David Johnson.

Who?

Probably underrated by most and perhaps still unknown by some, the 24-year-old running back is the base upon which the Cardinals’ seventh-ranked offense is centered. The 6-1, 224-pounder has big-back power with little-back feet and receiving skills.

“It’s hard to compare him to anybody,” Vikings cornerback Captain Munnerlyn said. “He does a lot of great things, but to compare him to anybody? I don’t know anybody who plays like him in this day and age.”

In 14 regular-season games since becoming the starter as a rookie late last year, Johnson has 13 100-yard games from scrimmage while leading the NFL in yards from scrimmage (1,871), rushing yards (1,202) and total touchdowns (15). He had 123 yards on 24 touches in a Dec. 10 win over the Vikings.

“He’s a complete player,” Vikings safety Harrison Smith said. “He’s a big guy but moves really well, cuts really well, can catch the ball out of the backfield and breaks a ton of tackles.”

Johnson has surpassed 100 yards from scrimmage in nine straight games, a franchise record and the league’s longest active streak.

“I don’t think there’s a back in Cardinals history that can do the things David can do,” Cardinals running backs coach Stump Mitchell, a former do-it-all Cardinals back himself, told the Arizona Republic. “We all may have had things we did pretty good. But I think David can be the best back who ever put on the Cardinals uniform.”

Slow starts have contributed to the Cardinals’ underachievement this season. They have a league-low 14 first-quarter points and are one of only two teams, along with Jacksonville, that have yet to score on an opening drive.

Finishing games also has been shaky. Kicker Chandler Catanzaro did kick a game-winning 34-yarder as time expired last week against San Francisco, but he also missed game-winning attempts in the loss to the Patriots and the 6-6 tie with Seattle.

Johnson, meanwhile, is a long-shot kid from Clinton, Iowa. He came out of high school with only two college scholarship offers. He went to Northern Iowa over Illinois State, starting out as a receiver and finishing as a running back who wasn’t drafted until the third round.

Johnson and sisters Darnecia and Danielle are triplets. They’re the youngest of six siblings raised by a single mother, Regina Johnson, who battled addiction while struggling to feed and care for her kids when they were young. When the triplets were in grade school, they had to move in with an older sibling while Regina spent time in jail and a halfway house after a drunken driving conviction.

David, however, has expressed gratitude to his mother publicly for getting her life in order after that. Today, people who know Johnson in Arizona say he acts like someone who appreciates the good times because he hasn’t forgotten — nor is he bitter about — the bad times.

Johnson ranks fourth in rushing yards (760), first among running backs in receiving yards (453) and second in yards from scrimmage (1,213). He’s second among running backs in receptions (40) and third among all players in total touchdowns (10).

In last week’s victory over the 49ers, he had 101 yards from scrimmage with touchdowns receiving and rushing. He now has 23 career touchdowns in 25 games.

On Arizona’s first touchdown, Fitzgerald drew attention to the right side of the formation. Johnson released into the left flat and had an easy 3-yard touchdown reception against a linebacker who was too slow to match up.

On Arizona’s fifth possession, receiver J.J. Nelson drew a pass interference penalty 38 yards downfield. On the next snap, Johnson burst up the middle for an 18-yard touchdown run.

Two possessions later, on first-and-10 from the 49ers 14-yard line, Johnson ran a route into the end zone. An overmatched safety had little choice but to grab Johnson. The pass interference penalty gave the Cardinals the ball at the 1 and led to a field goal and a 20-10 lead.

“He’s bigger [than he appears], so if you look at him, you’ll be like, ‘Oh, man, this can’t be the guy who is wearing No. 31 who’s running the ball like that,’ ” Munnerlyn said. “A lot of guys are sleeping on his speed. But he can definitely bounce it to the edge and hit you with the home run. So we definitely got our hands full.”