Dixon turned a fast lap of 211.372 mph to top the six-hour session under the lights at Homestead-Miami Speedway.
Team Penske's Ryan Briscoe was close behind at 210.793, followed at 210.603 by 2007 series champ Dario Franchitti, newly returned from an aborted run in NASCAR to join Dixon at Target Chip Ganassi Racing.
"We've got a lot of momentum that we're coming off from last year as well and we're going to try to keep that going," Dixon said. "You have to strike while the team's hot and team's doing everything right at the momentum. You can see right from the first session we're right where we need to be."
Franchitti said, "I'm still very much in the first stage of sort of getting used to the car again. But I'll be fine."
Twenty-one cars made runs on the 1.5-mile oval, with Dan Wheldon, another former champion, expected to make it 22 in Wednesday's session. Wheldon missed the Tuesday session due to a previous commitment.
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