Jimmie Johnson was comfortably in front when he blew a tire with seven laps left, precipitating the wild finish. Jeff Gordon moved in front until Clint Bowyer spun with two laps to go, setting up an overtime finish.
Gordon was hoping to finish on old tires when Bowyer spun, but then elected to pit along with most of the leaders. Kurt Busch gambled with just two tires, allowing him to restart in second, but his younger brother came up from fifth in the final two laps to win.
"I came off the fourth turn in disbelief that we won this thing, because we were mediocre all day," Kyle Busch said. "It was really weird for us, not a race that we're typically used to. But now there's a load off your shoulders that you can go out the rest of the season and race the way you want to."
He barely held off Larson, the 21-year-old rookie who held off Kyle Busch on Saturday to win the Nationwide race.
"I don't know where everybody went, but I somehow ended up in second and it entered my mind, 'We might sweep the weekend,'" Larson said.
He had to settle for the best finish of his Sprint Cup career in the No. 42 Chevrolet for Chip Ganassi Racing.
Kyle Busch, who went to Larson's car Saturday to congratulate him on his Nationwide win, pointed out his window at Larson after Sunday's finish, pumping his fist in approval.
"What a shoe that boy is," Kyle Busch said of Larson.
Several teams had serious tire problems on this weathered 2-mile oval, with multiple flats and cautions for various problems throughout the hot afternoon. The problems likely were the latest effect of NASCAR's new aero rules, which are producing higher speeds that lead to extra stress on the tires particularly on the bumpy asphalt on Fontana's back straightaway.
Those problems might frustrate pit crews, but they can also lead to phenomenal racing, as the sellout crowd on its feet for the finish could attest.
"By no means is this a problem for Goodyear," Kurt Busch said, referring to NASCAR's tire manufacturer. "It's just a thumbs-up for NASCAR for allowing teams to get aggressive in all areas."