Busch became the first driver in NASCAR history to win two national touring races on the same day, after his victory at the 200-mile truck event earlier in the day.
Busch had to overcome late-race challenges from Carl Edwards and Kevin Harvick in the Nationwide race to assure his record-setting day. He and Harvick caught Edwards just after a restart with 16 laps to go, and Busch won the race on the backstretch in the last lap.
"To run like that (at the Auto Club Speedway) and beat guys like Carl and Kevin, it's pretty special," Busch said. "To win here twice in one day, that's even more special."
David Ragan and Brian Vickers finished in a tie for fourth place in the Nationwide race.