Washington running back Adrian Peterson (26) runs up the middle during the first quarter of Friday’s loss to the Broncos. (John McDonnell/The Washington Post)

Considering all the juking, trucking and blazing that Adrian Peterson has done in his football career, one impressive preseason performance shouldn’t be worthy of fuss. He has been better. He has been superhuman. And this was only the preseason. Yet for all the qualifiers and attempts at measured evaluation, it was impossible not to feel something — encouragement? nostalgia? childlike enthusiasm? — as the future Hall of Famer turned his Washington Redskins debut Friday night into irrefutable proof that he belongs on this tailback-needy roster.

You thought the rest of this preseason would be an extended tryout for Peterson? Well, the tryout ended here at FedEx Field. Peterson unofficially made the team in less than a half of action during Washington’s otherwise listless 29-17 exhibition loss to the Denver Broncos. He probably ascended to starter on the depth chart, too, and even if Coach Jay Gruden needs to see more, it’s now safe to expect Peterson will be the lead back by the time the team takes the field in Arizona in Week 1. That’s how bad the running back situation is with Derrius Guice out for the year with a knee injury and two other rushers on the mend. But that’s also how well Peterson played in seizing this opportunity after waiting by the phone until late August for a job in a league he once ruled.

During this audition, Peterson rushed 11 times and gained 56 yards, including gains of 13 and 15. That 15-yard run came on his last carry of the night, a fourth-and-one play in which Peterson sprinted left, danced and rumbled for a first down that awoke the team and its fan base from customary preseason indifference. After the play, left tackle Trent Williams, his Oklahoma brother, ran onto the field to hug Peterson. And while there are thousands of examples I can give to caution you against getting too excited, there’s nothing wrong with believing in what you saw on a most basic level. Peterson still has some juice. He’s not an elite NFL player anymore, but he certainly isn’t a fringe one, either. Call him a has-been if you must. However, for this team, that might be better than relying on a bunch of mediocre never-haves for an entire season.

Peterson took it as an important step in his bid to make another comeback. In the past, he has been charged with reestablishing himself after injury, after suspension and after a child abuse revelation that left his reputation rightfully tarnished. But he’s still here, at 33, trying to be better and hoping to end his career on his terms. He seems certain now to get that chance in Washington.

“I saw a big guy running pretty hard, really,” Gruden said.

When I asked Peterson if he sensed he had made an impression, he said: “Not really, but it’s me just taking advantage of the opportunity, coming in and setting the example for the young guys and making the guys on the defensive side better as well. And the offensive line as well, with just how I approach practice. It’s my mentality going on 12 years now, and so for me, it’s the norm.”

Give Peterson credit for continuing to be a workout warrior this late in his career and maintaining focus during a frustrating and long wait in free agency. From the moment he joined the team for a workout Monday, he was ready not just to sneak onto this roster but to convince the coaches that they needed to adjust their plans.

I still believe that, for Peterson to be successful, healthy and productive here over a 16-game season, he will need to accept a more specialized role than he wants. But until he is told he must do that, it’s only right that Peterson fight for all that he wants. Right now, his drive can only help the team.

When asked this week if he was competing for the starting job, Peterson said: “Without a doubt. And I would be cheating myself if that wasn’t my approach.”

Gruden now has to balance letting Peterson test the limits with figuring out a role for him that best suits this team. He’s a creative and flexible offensive mind. If Peterson buys in, Gruden can be clever in devising a way to keep Peterson feeling active in a running back-by-committee approach without becoming predictable. For now, the coach is content to let the aging player try to prove he’s still a superstar.

“I wouldn’t tell Adrian that he’s not that,” Gruden said. “I think he is fully confident that he’s still the same guy he once was. On the hook, he looks pretty good. I think the key, really, is for any veteran to come in here and, No. 1, you have to set a great example for the young guys and to be good teammates, good leaders, not based on vocal leaders but leaders by example.

“When you see the type of physical condition he’s in, and Vernon Davis and Alex Smith are in, it’s an unbelievable example for the young kids of what it takes to be a professional athlete for this long a period of time. It just sets a good standard, a good tone, for the rest of these guys’ worth ethic. I think it’s great to have him here for however long it is. We relish the opportunity.”

In a small way, in a meaningless game for most, Washington received a glimpse of what Peterson is now. And it also experienced a feeling that never gets old: the excitement of watching Peterson when he gets in a groove. It’s an amazing, addictive thing. Even the defensive opponents whom Peterson has embarrassed end up being appreciative that they were on the field with such greatness.

“You never forget it,” Washington linebacker Mason Foster said.

Foster remembers facing Peterson as a Tampa Bay Buccaneers linebacker. It was 2012, the season that Peterson rushed for 2,097 yards on his way to the league MVP award. It was late October, the second of a 10-game stretch in which Peterson rushed for a ridiculous 1,598 yards. The Bucs were intent on keeping Peterson in check, and they did for most of the game. Then he ran for a 64-yard touchdown in the third quarter.

“We had been on him all game,” Foster said. “It was a big emphasis to keep him in check. Then I remember me and Lavonte [David] chasing him. He’s been a beast, man. He’s always been one of my favorite players to watch, so it’s pretty cool to have him here.”

It’s probably even cooler to know he’ll be staying for a while. This isn’t one of those same-ol’-Redskins, chase-the-big-name attempts to cheat player development and get ahead. This isn’t like the Bruce Smith or Deion Sanders acquisitions. This isn’t like trading for Donovan McNabb. It’s different because those were moves the team boldly and foolishly made thinking they were making a splash. Peterson was an emergency pickup. The team was fine going with young running backs until the injury bug ruined those plans.

There’s a lower risk to this Peterson reclamation project. Expectations are on a leash. If he fails, it won’t be all that jarring.

But what if he succeeds? After Friday, it’s now acceptable, at the least, to consider the possibility.