Nearly three years after a NASCAR ruling denied him his first Sprint Cup victory, Regan Smith finally got the elusive win.

After staying out on old tires, Smith held off Carl Edwards to win Saturday night's Showtime Southern 500 at Darlington Raceway in a dramatic green-white-checkered-flag finish.

Smith crossed the finish line .196 seconds ahead of runner-up Edwards. Moments later, tempers flared between drivers Kyle Busch and Kevin Harvick and their crews in the aftermath of a wild wreck that brought out the final caution of the race.

"This is the Southern 500 -- we're not supposed to win this thing," an incredulous Smith radioed to his crew after the race.

Brad Keselowski, also on old tires, finished third, with pole-sitter Kasey Kahne running fourth and Ryan Newman fifth.

The victory was redemption for Smith, who was deprived of an apparent victory at Talladega in 2008 when he was penalized for passing Tony Stewart below the yellow out-of-bounds line that separates the racing surface from the apron.

"This is no knock against Talladega at all, but I would trade in a lot of Talladega wins for one win in the Southern 500," said Smith, who got enough of a push from Keselowski on the final restart to clear Edwards' car. "This race is so special and so meaningful. We were standing there looking at the names and the faces on the trophy, and you just look at it, and you think, 'My face is going to be there right next to these guys, and it'll be there forever.' "

After a final round of green-flag pit stops, Edwards, the Cup points leader, passed Kahne for the lead on Lap 341 of the scheduled 367-lap race as the cars sped into Turn 1. Edwards was comfortably in front when Jeff Burton's engine blew and oiled the track with 10 laps left, causing the 10th caution of the night.

After Smith, Keselowski and Stewart stayed out, taking the top three spots under caution, Edwards climbed to second after a restart on Lap 363. The previous caution, however, was only a prelude to a wild three-wide wreck involving Clint Bowyer, Harvick and Busch later that same lap. That set up the two-lap sprint as the race went to overtime, with Edwards and Smith taking the green flag side-by-side.

Bowyer sustained the most damage as he hit the inside wall nose first. But as Busch and Harvick continued down the track, the two made contact again, with Busch spinning Harvick's car. After the race, Harvick confronted Busch on pit road and appeared to take a swing at Busch while he still was in his car. Later, while Smith was celebrating in Victory Lane, the crews from each team confronted each other.

Tempering the disappointment of finishing second for Edwards was his happiness for Smith, with whom he had established a friendship during their tenure with team owner Mike Mittler in 2002.

"I was driving Mike's truck," Edwards said. "I had run I think seven races and I couldn't run any more and still hold the rookie eligibility for the next year, so Mike hired Regan to drive at Phoenix. I was kind of heartbroken. I was a race car driver. I didn't want to go work on that truck while somebody else was driving it.

"I went there and I felt kind of honored when it was all over, to have worked with him and met his family. They're really good people. I just decided, all right, I'm going to go ahead and work, swallow my pride. I'm glad I did, because I got to know Regan a little bit better and he's a good guy.

"He could have treated me any way and he treated me like gold then, so I got a lot of respect for him."

Kahne, Edwards and Harvick took turns out front during the second half of the race after Busch made an unscheduled pit stop.

Busch had led 78 laps when a vibration forced him to the pits on Lap 205. A caution for Jimmie Johnson's spin on the frontstretch trapped Busch a lap down. Busch didn't get the lap back until he received a free pass as the highest scored lapped car for a restart on Lap 244.

Busch had worked his way up to 12th before NASCAR called the ninth caution on Lap 280 for debris on the backstretch. He finished 11th.