Dixon held the lead and Power was second when the two drivers pitted on lap 65, but after numerous video reviews, race officials determined Dixon had crossed into Power's pit box, where his car bumped into one of Power's crew members.
The impact caused the crew member to fall into two compatriots. All three were slightly injured in the incident.
Dixon exited pit road with Power close behind, but he was assessed a drive-thru penalty after a restart with 15 laps to go, allowing Power to take the lead.
Power retained the lead the rest of the way, beating Justin Wilson by 1.2 seconds during four-lap sprint to the finish for his 19th career IndyCar victory, breaking a 25-race winless streak.
Dixon ended up finishing 15th.
Points leader Helio Castroneves increased his lead over Dixon to eight points with a seventh-place showing.