Dixon tied an IndyCar Series record with his third consecutive victory at Nashville Superspeedway and teammate Dan Wheldon finished second as the race was red-flagged after 171 of 200 laps complete.
It was the 100 automobile racing victory for Chip Ganassi Racing (22 in the IndyCar Series), and Dixon held aloft his third hand-painted Sam Bass / Gibson guitar trophy.
"If I learn how to play, it might be bad luck," said Dixon, who tied Wheldon's record with three victories at the same venue. "It's a big night for Target Chip Ganassi Racing. Every time we ran this car I've won with it here at Nashville and at Watkins Glen. It's been a hell of a lot of luck for us, but you could not have been luckier than we were tonight.
"It was a miscommunication on the pit call. That's the only reason that I didn't come in. I was angry for a few laps, but when I saw that rain coming down, I thought, 'Oh, this could work out pretty good.' ''
The last rain-shortened race was the 2007 Indianapolis 500, won by Dario Franchitti. Tony Kanaan came out on the short end of both races.
Kanaan, driving the No. 11 7-Eleven car, led Dixon by 3.7595 seconds on Lap 136 and led the parade to pit lane on Lap 148 under yellow.
"It was the right call," Kanaan said. "Who can predict the rain? Unfortunately, the rain and I don't get along too well. But the 7-Eleven guys have great momentum and the guys at the front know we are coming. I'll take fourth place."
Dixon and Wheldon, who last pitted on Lap 102, held off the charges of Castroneves, Kanaan and Danica Patrick after the race resumed on Lap 152. The yellow flag flew for the final time on Lap 166.
"When it is your year, it is your year. You have to get a little lucky to win the championship and I got my share of the luck in 2004."
Dixon's fourth victory of the season - coupled with pole sitter Helio Castroneves' third-place finish - lifted his points lead from 48 to 63 points over the Team Penske driver. Danica Patrick, who joined Castroneves on the front row, finished fifth and Panther Racing's Vitor Meira advanced nine positions to sixth.
"It's not the race we wanted to have, especially the way it finished," Castroneves said. "I was told that the Ganassi guys had four laps of fuel left. That's two minutes. If the rain had come two minutes later, we would have won the race. But sometimes you have to be lucky than good. They did that and there's nothing we could do. Team Penske did its race and we finished third. If was good enough for what we had. The car was really tough to handle and third is good enough for the championship."
Buddy Rice, driving the No. 15 Dreyer & Reinbold Racing car, posted his second consecutive top-10 finish in seventh. Ed Carpenter, driving the No. 20 Menards/Vision Racing car, finished eighth and Darren Manning scored his second top 10 in a row for A.J. Foyt Racing in ninth.
Mario Moraes, who finished a career-high seventh last week at Watkins Glen International, was 10th.
"The car started to get pushy on us late in the race, but that was because the track was getting better," said Meira, who recorded his best finish since Texas in early June. "After the bad stretch we've been through, this is just what we needed to rebound. We have been solid everywhere we've been, it's just a matter of staying out of trouble. It was a race against time tonight, and a nerve-racking race, but we made some calls and it ended well."