Grosjean went 1 minute, 47.6781 seconds in his Dale Coyne Racing with RWR Honda on the 14-turn, 4.014-mile road course, where he tested two weeks ago.
“When you lead a free practice, you don’t want to make many changes for the rest of the weekend,” Grosjean said.
“The teams apparently are saving money on doing the shortened schedule because it’s one less day in hotels, things like that.
Kevin Magnussen, meanwhile, turned his first laps in an Indy car in the practice session as the replacement driver for Felix Rosenqvist, who was injured in a crash last week at Detroit.
His full-time job is driving the IMSA sports car for Chip Ganassi Racing, but the team gave him permission to race for Arrow McLaren SP this weekend.
“It’s never been a secret that IndyCar is something that I am pretty passionate about,” Magnussen said.
He’s joined in the field this weekend by Cody Shane Ware, who races mostly in NASCAR this year and will make his debut as Grosjean’s teammate.