The race at the Daytona International Speedway was halted for over an hour with 78 laps remaining while workers repaired a pothole that developed in the track.
The hole reappeared 39 laps later, forcing another 45-minute delay before racing resumed.
“It’s unbelievable. I can’t explain it,” a tearful McMurray told reporters.
“When I saw the No. 88 (Earnhardt’s car) behind me I thought ‘Oh, no.’ He had a good car and I just thought, Earnhardt at Daytona… They win all the time it seems like. So you just never know what to expect.”
A push, however, from former team mate and third-place finisher Greg Biffle helped McMurray take the lead after a second attempt to finish the race under a green flag.
“I spun my tires on the restart,” said McMurray. “Biffle gave me an unbelievable push on the backstretch.”
Earnhardt, who won the race in 2004 to join his late father as a Daytona 500 champion, roared from 10th on the second restart to challenge McMurray.
“It was all a blur,” said Earnhardt of the finish. “I was just going where they (other cars) weren’t. It went by so fast I couldn’t tell you the process.”
Clint Bowyer finished fourth, followed by David Reutimann, Martin Truex Jr. and Kevin Harvick.
A series of late accidents sent the race into an eight-lap overtime before McMurray took the checkered flag.