With a new contract, sponsor extensions and a solid one-car team at JTG Daugherty Racing, Allmendinger became a winner in Sprint Cup for the first time on a somber Sunday, outdueling Marcos Ambrose in the final two laps at Watkins Glen International.
"I dreamed about this moment and I'm not going to forget it," said Allmendinger, making his 213th Cup start. "It's just a dream come true."
The day began on a solemn note when three-time Cup champion Tony Stewart pulled out of the race 12 hours after he struck and killed 20-year-old sprint car driver Kevin Ward Jr. in a race after Ward climbed from his car on a small dirt track in nearby Canandaigua.
Allmendinger offered his condolences to the Ward family after he won, saying, "We're a community here, we're thinking about you."
"It's a tough time for everybody," Allmendinger said. "This NASCAR community, as a whole, we're a family. When anything like that happens, it's something that you don't get time to erase and forget about. Our thoughts and prayers go to the Ward family and what happened.
"And it also goes to Tony. It's not like he's sitting there and forgetting about it."
In a statement released during the race by a spokesman, Stewart said: "There aren't words to describe the sadness I feel about the accident that took the life of Kevin Ward Jr. It's a very emotional time for all involved, and it is the reason I've decided not to participate in today's race at Watkins Glen. My thoughts and prayers are with his family, friends and everyone affected by this tragedy."
Regan Smith drove Stewart's car and finished 37th after having to start from the back of the 43-car field and getting caught in a late accident.
It was the second straight time Stewart missed the race at The Glen, where he has a NASCAR-record five victories. Last year, he broke his leg in a sprint car accident in Iowa days before the Cup race and missed the rest of the season.
Allmendinger's life changed two years ago in the hours before the July race at Daytona International Speedway. NASCAR officials had just kicked him out of the track, suspending Allmendinger indefinitely for failing a random drug test.
The failed drug test sidelined him for more than three months and cost him his job with Penske Racing. It also spurred much soul searching, and after a handful of one-off Cup rides he eventually landed a full-time Cup ride last August with JTG Daugherty Racing.
To break through the way Allmendinger did only added to the lore of this race, which has been decided four straight times by fender-banging dashes to the checkered flag. Ambrose won two of those and Kyle Busch the other.
An expert road racer from his days in open-wheel, Allmendinger beat the best in Ambrose, who has been dominant in NASCAR's top two series at The Glen, also winning four straight Nationwide events.
Ambrose was going for a weekend sweep after capturing the Zippo 200 on Saturday.
"I'm thrilled for AJ," said Ambrose, who drove for JTG Daugherty before Allmendinger.
The victory made JTG Daugherty Racing eligible for the Chase for the Sprint Cup title, and Allmendinger isn't planning on stopping there.
"It's huge to be in the Chase," he said. "I didn't want to just say, 'Just be there.' We want to make some noise. To be able to say we're a Chase team, we're working hard and trying to get it back. When it comes to the Chase with the new format, it doesn't mean we can't get hot early. You don't have to be amazing for 10 races."
Allmendinger held off Ambrose through the first two turns on the final restart and opened a lead after both cars bumped and won going away.
"I try to get better every day. I'm still not where I want to be," Allmendinger said. "I wouldn't want to go back and change the process. I wouldn't change a thing about this."
There were three restarts in the decisive closing laps.
Allmendinger got the jump on Ambrose in the first one with nine laps to go, but Jimmie Johnson was bumped in the first turn and his No. 48 spun around, collecting two other cars and precipitating a caution.
The race restarted again with five laps left and both Ambrose and Allmendinger were side-by-side through the esses, banging against each other before Ambrose took the lead in the chicane as he's done so many times in the past, dirt flying as both cars hit the grass.
Allmendinger wasn't done, regaining the lead on the next lap as he out-braked the Australian into Turn 1 before a crash involving Denny Hamlin caused another red flag with four laps left.
The 90-lap race on the 2.45-mile layout was red-flagged for 1 hour, 21 minutes just past the midpoint after a violent crash involving Ryan Newman and Michael McDowell that involved three other cars.
Newman's Chevrolet spun hard into the Armco barrier lining the track, ripping a big hole in the barrier's metal. The car then spun around twice and went back across the racing surface, collecting McDowell in his No. 95, which incurred heavy damage in the rear. Newman, McDowell and Alex Bowman were treated in the infield care center and released.
Allmendinger gained the lead on Lap 64 after pit stops, with Kurt Busch and Ambrose close behind.
Ambrose outbraked Busch into Turn 1 for second two laps later and set his sights on Allmendinger, who had a 2-second lead that was wiped out by the late stoppages.
Jeff Gordon started from the pole and led the first 29 laps, holding Ambrose at bay. But Gordon's engine died on lap 50 as he lost all power and couldn't get it refired, spoiling a promising day.
Allmendinger Wins At Watkins Glen
AJ Allmendinger held off Marcos Ambrose to pick up the victory at Watkins Glen.
Allmendinger Gets First Career Win
AJ Allmendinger discusses winning his first career Sprint Cup race at Watkins Glen.
The Rundown: Watkins Glen
Brad Keselowski and Kyle Larson comment on their performances at Watkins Glen.