Johnson, who took the season-opening Daytona 500 in February, won the superspeedway's 400-mile event as well, leading 94 of 161 laps on his way to a 0.108-second victory over second-place finisher Tony Stewart.
The Hendrick Motorsports driver pulled off a Daytona sweep for the first time since Bobby Allison accomplished it 31 years ago.
His fourth win of the season came after an accident involving Hendrick teammate Kasey Kahne necessitated a two-lap overtime finish, during which Johnson pulled away from the pack.
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