NEW YORK — Ever seen a champagne celebration after what would normally be an excruciating walkoff loss?

We saw one Wednesday night at Yankee Stadium.

The Red Sox completed their latest worst-to-first saga when they clinched the American League East thanks to Baltimore’s 3-2 victory over Toronto.

It looked like the Sox were going to clinch with their own win over the Yankees (six one-hit innings from Clay Buchholz), but that did not happen. Minutes after learning that they were AL East champs by virtue of the Orioles’ win, Red Sox closer Craig Kimbrel allowed a single and three straight walks to start the ninth then watched helplessly as Mark Teixeira hit a game-winning grand slam off Joe Kelly.

It was just plain goofy. The stunned Sox, losers by a count of 5-3, came off the field, quietly exited their dugout, then went back to the clubhouse where goggles and bottles of champagne waited for them. Sox lockers (and several media members) were draped in plastic and the bubbly started to fly as music blared and players exclaimed, “AL East champs, baby!’’

Weird. It was like leaving a cemetery and walking into a Delta House toga party. Something tells me that Bill Belichick would not have approved.

“It was crazy,’’ David Ortiz said during the celebration in the clubhouse. “I wanted to celebrate on that field so bad. But it is what it is — at the end, being the first-place team in the American League East, we’re going to celebrate anyway. Let me pop! Let me pop a little bit!’’

On this night, the losers’ clubhouse was wild with delight. There was no filter and no seven-second delay for the champs. F-bombs flew freely on live television. Kelly, who had been trying to record his first big league save when Teixeira took him deep, said he was unaware the Sox had already clinched until he got back into the locker room. It marked the ninth time the Red Sox have won the AL East, and only the second time they did it on the road.

“We’re more than happy,’’ said Ortiz, who has a chance to win a fourth World Series before retiring next month. “At the beginning of this year, I knew we were going to do good offensively. But I didn’t know all these guys were going to progress that fast.’’

All those young guys. Mookie Betts. Xander Bogaerts. Jackie Bradley Jr. Andrew Benintendi. Through the drafting and player development of departed Theo Epstein and Ben Cherington the Sox have assembled the finest cast of young everyday talent in the majors. Picking up the torch, Sox second-year president of baseball operations Dave Dombrowski plugged the remaining holes through trades and free agency, and now John Henry’s Red Sox are back in the postseason tournament.

“It’s great, absolutely,’’ said Dustin Pedroia. “This is what you play for. This is the time when all the hard work really pays off. I think everyone’s expectation every year is to show up and try to win the World Series. If you don’t feel like that, what’s the sense of playing? We’ve got a ton of talent. It was just a matter of putting it all together.’’

The Sox have to win three rounds of playoffs to get where they want to go. They’ll start next Thursday — site and opponent yet to be determined. Step one was winning the division.

Watching the Sox celebrate inside Yankee Stadium conjured memories of 2004, when so many of the ghosts of 86 years were purged. That was the night the Yankees rolled over against the Red Sox in Game 7, then allowed Curt Schilling, Pedro Martinez, Johnny Damon, and friends to dance and pop bubbly on the sacred lawn of The House That Ruth Built.

This time the Sox celebrated inside a new Yankee Stadium, after losing to a far less formidable team, and playing in front of only 35,520. The single common denominator was Ortiz.

Big Papi was the center of the Red Sox universe when the Sox won in New York in 2004. Thursday he was in the middle of the cameras that crushed the clubhouse space on the visitors’ side of the stadium. He is hitless in two games in New York this week and will be honored before the series finale at the Stadium on Thursday.

“It’s unbelievable, man,’’ Ortiz said. “We’ve come a long way from where the season ended last year. Being able to be in the playoffs right now is something very special. Definitely. Definitely.

“It’s going to be my last one. I’m going to try to enjoy it the most I can.’’

Sox bosses Henry, Tom Werner, Sam Kennedy, Dombrowski, and GM Mike Hazen were all on hand for the clinch party.

Bogaerts, who won’t turn 24 until this weekend, was part of the championship ride three years ago, then lived through the back-to-back last-place finishes. He appreciates this perhaps a tad more than the other kids.

“I thought I was going to make the playoffs every year,’’ admitted the shortstop. “I made it the first year so I thought it was something that was going to happen often.’’

It does not happen that often. Baseball is not easy. Baseball is hard.

“No one likes to finish in last place,’’ said manager John Farrell. “It’s been a journey. You learn to relish the good times a little more. It’s meaningful. We’re on the cusp of doing something special.’’

Dan Shaughnessy can be reached at dshaughnessy@globe.com