Miscommunication kept Dixon from pitting along with leader Tony Kanaan, helping him grab the lead.
"When they called me to pit, or follow Kanaan was the words, I was way past ... there was no coming in," Dixon said as he cradled the trophy Gibson guitar under cover.
"It worked out fantastic. I'm bloody happy for the championship to be honest," said Dixon who won the series as a rookie in 2003.
Indy Racing League officials hoped to squeeze in at least 101 laps to make the race official with rain on the radar. This race was washed out a year ago and run on Sunday with lots of empty seats.
The third caution of the night came on lap 139 when the rain finally hit. The cars kept rolling even as fans were asked to evacuate the grandstand immediately due to weather. They went back to green before the fourth and final caution came on lap 167.
IRL officials kept the cars rolling until the rain came harder, and the race was red-flagged on lap 171. Officials checked the radar, which showed heavy rain stretching out far to the west. This race became the 13th IndyCar Series event with a red flag, the first since the Indianapolis 500 in 2007, and the fourth red-flagged and not restarted because of rain.
Dixon earned his fourth victory of the season, his 14th of his career, and the 100th overall in motorsports for Chip Ganassi
He also extended his lead over Castroneves in the points race from 48 to 63.
It was a nice change from a week ago when a mistake at Watkins Glen cost Dixon a chance at victory and dropped him to 11th.
"I'd like to keep winning more so everyone would forget about that," Dixon said.
Ganassi teammate Dan Wheldon finished second after gambling that he could stretch his fuel until the rain hit. It was the 26th time in IndyCar history that teammates have finished 1-2, the fourth time for Target Chip Ganassi.
Pole-sitter Helio Castroneves took advantage of a track cleaned of the rubber chunks chewed off the tires by the concrete track to pass both Danica Patrick and Kanaan on lap 153 after the last restart. He finished third.
Kanaan wound up fourth and Patrick fifth.
Castroneves started on the pole, the first he had earned in qualifying this year.
The Brazilian looked strong early but lost the lead on lap 55 when Dixon passed him with Kanaan and Patrick coming with him. At least Castroneves led a lap on this track for the first time in seven starts, leaving Sonoma as the only track where he has never led at least one lap.
He called it a tough night.
"It's one of those days. Those guys had what, 10-15 laps on the fuel (left)? They took a chance. Chances sometimes pay off. It paid off for those guys. We did everything we could, and third-place is not bad. We're still in the championship hunt. We're going to keep working hard," Castroneves said.
