Rookie Santino Ferrucci was fastest in the first practice session for the Bommarito 500 at World Wide Technology Raceway at Gateway Friday afternoon, posting a lap of 184.804 mph (24.3501 seconds) around the 1.25-mile oval.
Fellow IndyCar rookie Marcus Ericsson ended the session second-fastest with a 184.527 mph. Championship contender Scott Dixon finished the session third fastest at 184.433 mph.
Current IndyCar point leader Josef Newgarden was fourth-fastest with his 184.348 lap, while Sebastian Bourdais finished the session fifth-fastest with a 184.123 mph lap.
Alexander Rossi (183.658 mph) and Will Power (183.607 mph) ended the session sixth and seventh fastest, respectfully, while Takuma Sato (183.593 mph), Ryan Hunter-Reay (183.177 mph), and Colton Herta (182985 mph) rounded out the top 10.
Indy 500 winner and championship contender Simon Pagenaud finished the session 14th-fastest with a 182.342 mph lap.
Live coverage of Bommarito Automotive Group 500 qualifying begins later this evening at 6 p.m. ET on NBCSN.