Scott Dixon went quickest in the third IndyCar practice session around the Belle Isle street circuit.
The Target Chip Ganassi racer took turns with Penske rival Will Power at the top of the timing screens throughout most of the session before finally trumping the Australian with a 1m11.2845s; 0.18sec better than Power could manage.
Andretti's Ryan Hunter-Reay overcame a 1m stop-and-hold penalty for an unsafe pit release to set the third-fastest time. Hunter-Reay was released from his pit box into the path of Penske's Ryan Briscoe, causing the pair to bump wheels in pitlane. Neither car came to any harm, and Briscoe went on go fourth fastest.
The morning got off to a stuttering start with a flurry of three early red flags in quick succession, the first being triggered by Briscoe spinning on his out-lap.
Dreyer & Reinbold's Oriol Servia and last weekend's Indy 500 winner Dario Franchitti were the other two culprits, although only Servia made contact with the wall. The resultant damage prevented the Spaniard from taking any further part in the session.