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.