– He looks so young. Stefon Diggs will be 21 for a few more weeks, but he probably can’t get a drink anywhere in America without two forms of ID and a note from his birth doctor.

With his baby face and sleek outfit — black loafers, no socks, black pants, black turtleneck, gray checked jacket with a subtle patterned pocket handkerchief — Diggs could have passed for an aspiring jazz pianist playing one of the tonier Chicago hotels.

Sunday, the Vikings rookie saved his improvising for Soldier Field’s sandy turf, again displaying savvy beyond his years. For the third straight week, a fifth-round draft pick who was inactive for the Vikings’ first three games might have made the difference between winning and losing.

With the Vikings trailing by seven and the clock ticking toward three minutes remaining, Diggs made the biggest play of his young career, catching a pass from Teddy Bridgewater in the middle of the field, fooling the defense by reversing course and pushing through two defenders near the goal line for a 40-yard touchdown that tied the score.

Blair Walsh’s last-second field goal made it Vikings 23, Bears 20, giving the Vikings their first victory in Chicago since 2007 and a reminder that you can’t spell SOD (Steal of the Draft) without Diggs’ initials.

“What’s up, Dawg?” defensive end Brian Robison yelled to him in the locker room. “You could only get 95 today?”

“Sorry,” Diggs said with a smile.

Ask Diggs to explain his touchdown, and he reveals the depth of his studiousness, talking about how the defense changed at the last second, how he felt the defender shading him toward the inside of the field, prompting him to spin the other way.

He’s also smart enough to compliment the only man who can get him the ball.

“That was all Teddy,” he said.

Despite catching just one pass for 4 yards in the first half, Diggs finished with six for 95 and a touchdown. He has been active for four NFL games. In those he has caught 25 passes for 419 yards and two touchdowns. At that pace, over a 16-game season, he would catch 100 passes for 1,676 yards and eight touchdowns.

He almost enabled a comeback victory at Denver. He torched Kansas City, leading the Vikings’ defensive backs to project him as a Hall of Fame player. He caught a 36-yard touchdown against Detroit that turned the game in the Vikings’ favor.

Sunday, he showed off his catch-and-run moves and shades of his personality.

When Marcus Sherels returned a punt for a touchdown, Diggs, who wasn’t on the field, put on his helmet and sprinted toward the end zone to celebrate with him.

When Diggs scored his touchdown he went through an elaborate routine that seemed to include some sort of shoveling action, before screaming into a camera so violently that the cameraman backed away in fear.

When Diggs caught a short pass and wiped out on the Soldier Field “turf,” forcing him to limp off, he slammed his helmet violently before limping to the bench.

With Diggs sidelined, Charles Johnson, the young Vikings receiver who was supposed to break out this season, made a leaping catch to set up Walsh’s game-winner.

“It worked out for the best,” Diggs said. “I didn’t even like my touchdown as much as I liked CJ’s catch. That’s one of the best I’ve ever seen.”

It’s hard to tell whether Diggs was invented by a scout or a public relations executive. As a fifth-round draft pick, he might be the difference between the Vikings being 5-2 and 2-5. As a budding star, he’s gregarious and polite.

Sunday afternoon, as Diggs was smoothing out his outfit, Johnson stood next to him wearing a garish jacket featuring words like “Boom!” and “Ka-Pow!”

What would it take for Diggs to wear cartoon captions?

“That would take me a lot,” he said. “I’m more of a classic guy. But I love his jacket, still.”

Then Diggs smiled and told everyone to “have a great day.” He’s becoming an expert on those.