Championship rivals Alexander Rossi and Will Power were out front early in the race but Power suffered a transmission problem and fell out of contention.
Rossi looked like he would take a decent championship lead to the final round after leading for a big chunk of the race.
But Dixon, worked strategy perfectly to get himself back into contention and then pitted just prior to a caution, to leapfrog Rossi.
"I thought it was pretty bad," Dixon said as he went off the track. "I couldn't see anything – once I got into the dirt I kept getting hit.
"The suspension felt like it was a bit bent but a huge day for the team."
Dixon certainly got away with a major scare but he doesn't think it is time to celebrate a fifth title just yet.
"I dunno," he said. "Obviously going into Sonoma with 29 points is not a lot. I am really happy for the team. These girls and guys work so hard."