Dillon's 12th-place finish in Saturday night's Ford EcoBoost 300 was enough to edge Penske Racing's Sam Hornish Jr. by three points.
The 23-year-old, headed for NASCAR's Sprint Cup Series next season, entered the race with an eight-point lead.
Dillon's car was uncooperative in the early stages of the 200-lap event Hornish, in the meantime, refused to go quietly, running in the top five most of the night.
But a late-race swing ? the result of several caution flags ? bought Dillon time and track position.
When he crossed the finish line, he was quick to key his team's radio.
"Are we the champs?" Dillon asked. When no immediate response followed, Dillon repeated the question.
The answer ? a very loud "Yeah baby!" over the radio.
Hornish finished eighth in a race won by defending Sprint Cup champion Brad Keselowski, not quite enough in his final start for the Penske organization.
It is the second NASCAR title for Dillon, who won the Camping World Truck Series title in 2011. A year ago, he finished third in points and won Sunoco Rookie of the Year honors in the Nationwide Series.
Hornish was third, Dillon fifth when the field took the green for the final time, with five laps remaining. Both lost spots in the closing laps as drivers with fresher tires forced their way through the field.
Dillon called it "probably the worst car we've had all year," but said crew chief Danny Stockman Jr. "kept me positive in the car."
"I knew I just had to go on that last restart," he said. "I've been criticized for my restarts for a long time; that was a pretty good one. I just hung up against the wall there and tried to ride it out.
"For me, it's all about my guys in this one. Danny ? changed my career as a crew chief. He had confidence in me and (in) anything I told him from the beginning. ? He's stuck by my side and always given me speed in race cars.
"Tonight, more than anything, he gave me motivation and I've got to thank him for that. We didn't have the fastest car; it was ugly, the way we did it, but we showed we had heart."
Dillon, the first driver to capture the Nationwide title without winning a race, called Hornish "a great competitor."
"When you win them like this, it means so much more," the Richard Childress Racing driver said. "Tight, nerve-wracking all the way down to the end. I'm not going to lie, I was nervous."
A scrape with the wall (Lap 134) and a near miss when Brad Sweet and Justin Allgaier a bit later nearly swung the title in favor of Hornish, but Dillon persevered. The initial brush was a wake-up call, he said.
"I hit the wall once," he said, and told himself "you can either wreck here and give the championship away or wait till the end and give yourself a chance.
"That's what we did. We gave ourselves a chance. And it worked out for us."
Stockman, a part of championship winning teams with Ron Hornaday Jr. and Dillon in the truck series, called this year's title effort "by far the hardest one that I had to do.
"I mean we had to dig ourselves out of a serious hole tonight."
Having run through a laundry list of adjustments to the No. 3 Chevrolet in an effort to make his driver happy, and his car fast, Stockman said he was "out of tools to tighten the car up."
At that point, it was up to his young driver to bring it home and hope for the best.
"I couldn't do any more without really messing the balance of the car up too much," said Stockman. "I just stayed calm.
"I think the stress got so high that you just get used to it. You just kind of level out, deal with it. It's either crap or get off the pot. There ain't nothing else to do. Make it happen, right?"
At the end, he said, "I feel like we made it happen.
"Kind of ugly, but we did."
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