Indy 500 victor Takuma Sato, who was eighth on Sunday, is third overall with 258.
"It was a tough race no matter what", admitted Dixon, who's second place moves him to the top of the championship standings.
Team Penske's Josef Newgarden finished fourth and Alexander Rossi of Andretti Herta Autosport with Curb-Agajanian placed fifth, putting five different teams among the top five finishers for the first time in a race this season.
After being caught up in crashes at St. Pete and Phoenix, Rahal had another disappointing result last weekend at Indianapolis when he charged from 18th to third only to have a right rear tire go flat.
United States employers add modest 138K jobs; rate dips to 4.3 percent
Job gains for March and April were also revised down, showing 66,000 fewer jobs were added than first estimated. Yet the decline stemmed more from people leaving the labor force than an increase in the number who found jobs.
Helio Castroneves, who shared the front row with Rahal after his pole run was erased by IndyCar officials for not slowing enough under caution during qualifying, led 11 laps but abandoned a two-stop strategy and faded to seventh at the finish. The second race of the Chevrolet Detroit Grand Prix is scheduled for Sunday. Hinchcliffe spun around, hitting only the right-side barrier with light contact. Charlie Kimball couldn't avoid a slowing Conor Daly on the backstretch, and the contact that followed broke a piece of Kimball's auto. "We've definitely got to improve the auto - it's not ideal right now". As was the case in Hinchcliffe's situation, Kimball's spin came with only a bump of the wall.
It is also the first street-course victory by the Rahal team since co-owner Bobby Rahal won the inaugural Belle Isle race 25 years ago.
Unlike the other road and street courses throughout the year, qualifying around the streets of Detroit is rather unique, with the field split into two segments and the overall fastest driver securing pole position, with that driver's group forming the grid in the odd-numbered positions.
Driving the No. 15 Honda for Rahal Letterman Lanigan Racing, Graham Rahal set a Belle Isle record en route to winning the pole for this afternoon's first race in Detroit. The 70-lap race begins shortly after 3:30 p.m. ET on ABC.