The #12 Team Penske-Chevrolet driver set the fastest time on the harder compound primary Firestones with a 1min17.6869sec, before Alexander Rossi on a set of softer alternates edged ahead by just 0.03sec.
O’Ward initially couldn’t improve his time on reds, but then laid down a 1min17.5143. But that wasn’t enough to put him top as Sebastien Bourdais had delivered a 1min17.4291sec for AJ Foyt Racing-Chevrolet.
On reds, Power couldn’t improve for several laps, but three-time Detroit GP winner Scott Dixon could, and wound up fastest of the Honda contingent, ahead of Rossi, Herta and Dixon’s teammate Marcus Ericsson.
Then Power on his final lap produced a 1min17.2768sec lap around the 2.35-mile 14-turn course, 0.15sec than Bourdais.
Rinus VeeKay of Ed Carpenter Racing never set a time on primaries as he launched over the grass at Turn 1 and came back into the pits for a thorough checkover
Romain Grosjean in the Dale Coyne Racing-Honda with RWR-Honda spun on his 18th lap down at Turn 4, but managed to merely skim the advertising banner covering the tire wall, so spun-turn his car and continued. He eventually finished the session in 13th, 1.3sec off top spot.
Rookie Scott McLaughlin understeered into the tire wall at Turn 5 on his sixth lap, breaking his right front suspension and wing, which caused Jimmie Johnson to spin the #48 Ganassi – flat spotting his tires but keeping the car off the wall. McLaughlin described his own shunt as a “stupid mistake”, and it meant he missed the remainder of the session.
Alex Palou, championship leader, turned the most laps – 31 – but was only 15th.
Detroit’s Belle Isle course proved a tough nut for Palou’s teammate Johnson who ended up 5.4sec off the ultimate pace.