Rahal led for 55 of the 70 laps in Detroit to earn the fifth win of his 11-year IndyCar career and his first since last August in Texas.
Rahal covered the 2.36-mile, 13-turn temporary road course in 1 minute, 13.9681 seconds at 114.966 miles per hour. Other notable finishers were three-time Detroit champion Helio Castroneves, who finished in seventh place, and this year's Indianapolis 500 victor Takuma Sato in eighth.
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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.
Immediately after the first group had completed their qualifying runs an incident between Pagenaud and Sato was investigated by the race stewards, with Pagenaud in particular unhappy with Sato for slowing during the session. 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. The rescue crew got the auto righted so quickly he didn't lose a lap to the leaders. As was the case in Hinchcliffe's situation, Kimball's spin came with only a bump of the wall.
It had looked like Castroneves topped the field for the second straight day, winning the pole position with a track-record time of 1:13.890 on the 13-turn, 2.3-mile street course on Belle Isle. The pole is his first since 2009 and the team's first since 2007. Hopefully get some good rest tonight and obviously qualifying tomorrow is going to be key for the race. The Rahal Letterman Lanigan Racing driver proved it today with a dominant victory in the first race of the Verizon IndyCar Series weekend doubleheader.