A massive crash marred the final laps of the Daytona 500 … as 23 cars in total pinballed off each other in a wild mess toward the end of the famed race — although the carnage ultimately allowed underdog William Byron to come out with the win.

The chaos happened with eight laps to go at Daytona International Speedway in Florida … when Alex Bowman started the wreck by nudging Byron.

The bump caused Byron’s No. 24 car to slide into Brad Keselowski‘s … which set off a huge chain reaction of accidents.

Check out the replay from the race’s broadcast … more than half of the 40 vehicles in the field got caught up in the melee.

Somehow, Byron escaped it all unscathed … and after another set of drivers wrecked a few moments after officials got the track all cleaned up, the 26-year-old was declared the winner.

Afterward, he celebrated like crazy … telling reporters he couldn’t believe it all was actually happening.

The race, meanwhile, was delayed a full day … after rain forced NASCAR officials to move it from its usual Sunday start time to Monday.

While Pitbull could not perform his scheduled pre-race concert as planned … The Rock still made it out to the festivities — and fired up the crowd when he told the racers to start their engines.

Bubba Wallace finished the race in sixth place … while fan-favorite Kyle finished Buschended up 12th. Jimmie Johnson — a two-time Daytona 500 winner — nabbed 28th place after a wreck knocked him out early.