Alexander Rossi produced a strong lap on soft tyres to beat Penske drivers Will Power and Josef Newgarden to top spot in practice for IndyCar's Road America race.
Rossi was the first driver of the weekend to set a 140mph-average lap, recording a 1m43.1206s lap of the 4.014-mile track in second practice in his Honda-powered Andretti Autosport entry.
That effort put him 0.2883 seconds clear of Power, whose best time eclipsed Newgarden's by just 0.0669s. Both also set their times on the softer alternate compound.
Colton Herta was fourth fastest for Harding Steinbrenner Racing, just 0.0049s ahead of fellow rookie Felix Rosenqvist in the faster of the two Chip Ganassi Racing-Hondas, while Graham Rahal was sixth in his Rahal Letterman Lanigan Racing entry.
Ryan Hunter-Reay was seventh in his Andretti Autosport-Honda, having topped the first practice session, ahead of James Hinchcliffe, Patricio O'Ward (Carlin-Chevrolet) and Marco Andretti.
Simon Pagenaud was only 15th in the third Penske, just ahead of the two AJ Foyt Racing-Chevrolets.
Hunter-Reay's fastest time in an opening practice that was twice halted by red flags caused by Jack Harvey was a 1m43.7556s.
The first stoppage came after 20 minutes when Michael Shank Racing driver Harvey ground to a halt at Turn 12 with an electrical problem.
That issue was reserved, and Harvey returned to the track after serving a five-minute penalty for causing the red flag - only to suffer a stuck throttle at the same spot, before skating over the gravel trap and nosing into a tyre barrier.
Harvey's first off had shortened the original 30-minute period in which drivers were permitted to use their push-to-pass boost, which protected Hunter-Reay's place at the head of the order.
Takuma Sato ended up second in his Rahal Letterman Lanigan Racing-Honda, 0.0688s behind, ahead of Scott Dixon's Chip Ganassi Racing-Honda.
Power and Newgarden were fourth and fifth, with Rossi behind the two in that session.
|1||Ryan Hunter-Reay||Andretti Autosport||Dallara/Honda||1m43.7556s|
|2||Takuma Sato||Rahal Letterman Lanigan||Dallara/Honda||0.0688s|
|3||Scott Dixon||Chip Ganassi Racing||Dallara/Honda||0.2286s|
|4||Will Power||Team Penske||Dallara/Chevrolet||0.2838s|
|5||Josef Newgarden||Team Penske||Dallara/Chevrolet||0.3150s|
|6||Alexander Rossi||Andretti Autosport||Dallara/Honda||0.4283s|
|7||Simon Pagenaud||Team Penske||Dallara/Chevrolet||0.6423s|
|8||Spencer Pigot||Ed Carpenter Racing||Dallara/Chevrolet||0.6468s|
|9||James Hinchcliffe||Schmidt Peterson Motorsports||Dallara/Honda||0.6630s|
|10||Marco Andretti||Andretti Herta||Dallara/Honda||0.8307s|
|11||Sebastien Bourdais||Dale Coyne Racing||Dallara/Honda||0.8660s|
|12||Tony Kanaan||AJ Foyt Enterprises||Dallara/Chevrolet||0.9844s|
|14||Ed Jones||Ed Carpenter Racing||Dallara/Chevrolet||1.1494s|
|15||Felix Rosenqvist||Chip Ganassi Racing||Dallara/Honda||1.1973s|
|16||Colton Herta||Harding Racing||Dallara/Honda||1.2276s|
|17||Zach Veach||Andretti Autosport||Dallara/Honda||1.2902s|
|18||Matheus Leist||AJ Foyt Enterprises||Dallara/Chevrolet||1.6065s|
|19||Santino Ferrucci||Dale Coyne Racing||Dallara/Honda||1.8400s|
|20||Marcus Ericsson||Schmidt Peterson Motorsports||Dallara/Honda||1.8563s|
|21||Graham Rahal||Rahal Letterman Lanigan||Dallara/Honda||1.8636s|
|22||Jack Harvey||Meyer Shank Racing||Dallara/Honda||3.1529s|
|1||Alexander Rossi||Andretti Autosport||Dallara/Honda||1m43.1206s|
|2||Will Power||Team Penske||Dallara/Chevrolet||0.2883s|
|3||Josef Newgarden||Team Penske||Dallara/Chevrolet||0.3552s|
|4||Colton Herta||Harding Racing||Dallara/Honda||0.6209s|
|5||Felix Rosenqvist||Chip Ganassi Racing||Dallara/Honda||0.6258s|
|6||Graham Rahal||Rahal Letterman Lanigan||Dallara/Honda||0.8566s|
|7||Ryan Hunter-Reay||Andretti Autosport||Dallara/Honda||0.8930s|
|8||James Hinchcliffe||Schmidt Peterson Motorsports||Dallara/Honda||0.9217s|
|10||Marco Andretti||Andretti Herta||Dallara/Honda||0.9525s|
|11||Scott Dixon||Chip Ganassi Racing||Dallara/Honda||1.0453s|
|12||Zach Veach||Andretti Autosport||Dallara/Honda||1.0812s|
|13||Spencer Pigot||Ed Carpenter Racing||Dallara/Chevrolet||1.0889s|
|14||Sebastien Bourdais||Dale Coyne Racing||Dallara/Honda||1.1230s|
|15||Simon Pagenaud||Team Penske||Dallara/Chevrolet||1.3736s|
|16||Matheus Leist||AJ Foyt Enterprises||Dallara/Chevrolet||1.4655s|
|17||Tony Kanaan||AJ Foyt Enterprises||Dallara/Chevrolet||1.4845s|
|18||Takuma Sato||Rahal Letterman Lanigan||Dallara/Honda||1.4935s|
|19||Ed Jones||Ed Carpenter Racing||Dallara/Chevrolet||1.5394s|
|20||Santino Ferrucci||Dale Coyne Racing||Dallara/Honda||1.5786s|
|22||Marcus Ericsson||Schmidt Peterson Motorsports||Dallara/Honda||1.9427s|
|23||Jack Harvey||Meyer Shank Racing||Dallara/Honda||2.1211s|