Dixon moved to within 26 points of Will Power in the championship standings with the victory, which was first delayed for 2 hours due to poor conditions on the Detroit street circuit and then cut short by 30 laps as darkness fell.
Dixon finished ahead of Target Chip Ganassi Racing teammate Dario Franchitti, giving the team its second straight 1-2 finish. Franchitti won last week's Indianapolis 500 while Dixon was runner-up.
Chunks of asphalt came loose on turns six, seven and 10 of the 14-turn street circuit during the race. The contest was halted after James Hinchcliffe struck a loose piece, sending him into the tire barrier on turn seven.
The race was resumed after a lengthy delay for repairs and inspections.
Sarah Fisher Hartman Racing's Simon Pagenaud claimed third place while Team Penske's Power finished fourth.
Oriol Servia of Dreyer and Reinbold Racing completed the Top 5.