Sebastien Bourdais set the pace in a double-red-flagged practice one ahead of this weekend's Grand Prix of Portland, edging championship leader Scott Dixon to the top spot on the timesheets.
Bourdais, who heads to Oregon following a disappointing race at the Bommarito Automotive Group 500 last weekend, lapped the 3.12km-long circuit in 57.3975s, 0.0446s ahead of Dixon who ended the 45-minute-long session in second fastest after a mid-session spin.
Reigning IndyCar champion Josef Newgarden completed the top three in the #1 Team Penske Chevrolet and was followed by Marco Andretti as the highest placed Andretti Autosport driver in fourth, 0.3139s adrift of Bourdais' session-topping pace.
Championship hopeful Will Power completed the top five in the second Team Penske entry while he was closely followed by series rookie Jordan King who was sixth fastest for Ed Carpenter Racing.
Alexander Rossi followed King in seventh after treating FP1 as an acclimatisation session, heading to Portland this weekend with the aim of reducing Dixon's 26 point lead at the top of the Drivers' Championship.
Rahal Letterman Lanigan Racing's Takuma Sato set the eighth fastest time of the session, 0.3940 off the pace and was followed by Ed Jones in the #10 Chip Ganassi Racing car.
Rookie Zach Veach completed the top 10 for Andretti Autosport after bringing out the first of two red flags in the session.
Britain's Jack Harvey was 11th fastest while Santino Ferrucci put in an impressive performance, setting the 12th fastest time in the second Dale Coyne Racing car.
Alfonso Celis Jr caused the second red flag, ending the session as the slowest driver in 24th after Pietro Fittipaldi failed to complete a lap due to a brake problem.
