Decoding the most important play of the most important game of the season, Lions cornerback Darius Slay made the interception, turning what might have been a game-winning drive for the Vikings into an indictment of their football-in-a-phone-booth offense.

After Matt Prater’s field goal made the final score 16-13, giving the Lions the division lead, Bradford looked like a man seeking a portable curtain. He kept his helmet on and walked slowly to the middle of the field for the traditional starting-quarterback handshake.

This one lasted a millisecond. Lions quarterback Matthew Stafford sensed Bradford’s mood and moved quickly away.

Bradford walked slowly, helmet still on, flanked by security, across the field and toward the locker room. A Lions defender rushed up to greet him and Bradford again declined to discuss offseason travel plans, offering a brief shoulder tap without breaking stride.

All veteran NFL starting quarterbacks throw interceptions and lose games, but when the former leads directly to the latter, the quarterback can sometimes look after the game as if he has been tased.

“I think they’re all tough,” Bradford said. “Regardless of how they happen, a loss is a loss. I think they’re all pretty hard to swallow at first.”

But there is a difference between prune juice and arsenic, between what tastes bad and that which damages.

Bradford had excelled all day in lawn-sprinkler mode, spurting out passes as fast as shotgun snaps could reach his hands. He completed 31 of 36 passes before Slay stole the last one.

It’s difficult to complete 80 percent of your passes in flag football, much less on the road while playing for an NFL division lead, but this is what Bradford has done all season.

His offensive line is unrecognizable. His backs scare no one. His receiving corps was missing its best player, Stefon Diggs, and relying on a rookie, Laquon Treadwell, yet to earn his playing time.

Bradford knew he had to throw quickly. Often looking more like a second baseman turning a double play than a drop-back quarterback, he finished with 224 yards and just the one, damaging interception — one rooted in Vikings history.

The Cover-2 concept originated with Chuck Noll’s legendary Steelers. Tony Dungy adopted the strategy and popularized it with another former Vikings assistant, Monte Kiffin, and Leslie Frazier relied on it when the Vikings won the division in 2012.

For most of Thursday’s game, the Lions played man-to-man on the Vikings receivers, hoping to take away Bradford’s easiest throws.

With 38 seconds remaining and the score 13-13, the Vikings faced third-and-7 from their 28. They had just converted a third-and-2 with a 7-yard gain that was erased by an illegal-formation call.

Bradford dropped back, and Adam Thielen, lined up to the right, ran downfield and quickly cut to the right.

If the Lions had been playing man-to-man, Thielen would have been open and likely would have produced a first down, which would have given the Vikings a chance to drive for a game-winning field goal.

The Lions were playing Cover-2, or Tampa-2. Instead of turning and following his man, Slay read Bradford’s eyes and cut in front of Thielen. He made the catch, held on to the ball just long enough as Cordarrelle Patterson tried to rip it free, and gave the Lions the division lead.

“The corner made a good play,” Bradford said. “To my knowledge, that was the first time he did that today.”

“I’ve just got to do a better job of knocking that ball down,” Thielen said.

Given Bradford’s accuracy this season, the play was an aberration. Given the Vikings’ inability to threaten defenses with deep passes, it seemed inevitable. Bradford has little time and less margin for error, and anything less than perfection can cost him a game.

“We’ve probably got to find a way to create some explosive plays,” he said. “It’s hard when you are only picking up 5, 6, 7 yards at a time.”

Because Bradford had no margin for error, now neither do the Vikings.