Acura Team Penske's Dane Cameron claimed pole position for the IMSA SportsCar Championship race at Road America.
Cameron set a best time of 1m48.715 seconds that cut more than two seconds from the DPi record, as he turned the fastest Prototype lap at Road America since 2008.
Mazda Team Joest driver Oliver Jarvis split the Acura ARX-05s before the session was interrupted by a red flag caused by Matt McMurry dropping his LMP2 car into a sandtrap.
But when the action resumed and Helio Castroneves went out for the final five minutes, his last effort drew him to within 0.016s of Cameron to complete an Acura Penske front row.
Jonathan Bomarito was not so successful in finding a clean lap in the second Mazda and was disappointed to wind up 0.4s off team-mate Jarvis, but it was still quick enough to take fourth on the grid.
Simon Trummer earned the honour of being quickest Cadillac DPi-V.R driver in the JDC Miller Motorsports #84 entry but he was 1.2s off the ultimate pace in fifth, 0.2s ahead of Action Express Racing's Pipo Derani.
A brief rain shower between the abbreviated GTD and GT Le Mans sessions left some localised damp patches, one of which sent Jan Magnussen's #3 Corvette C7.R skating on at the final corner, although he dug himself out without assistance.
Magnussen's team-mate Oliver Gavin was the first driver to eclipse the GTD times, and it took until his third lap to do so.
Thereafter the track started drying rapidly, and Patrick Pilet's #912 Porsche took a turn at the top but then Tom Blomqvist's #25 BMW M8 set a new GTLM lap record at 2min00.344sec to take first place in class.
Gavin looked like he was going to be Blomqvist's closest challenger before Ryan Briscoe completed a strong lap in the final seconds to beat Gavin by 0.005s.
But the former IndyCar driver was adjudged to have exceeded track limits at Turn 1 and his lap was invalidated.
Briscoe was relegated to fourth, where he'll start alongside the second BMW of Jesse Krohn who was some 0.4s slower than his team-mate.
Dirk Muller (Ford) and Laurens Vanthoor (Porsche 911 RSR) followed, while Magnussen and Pilet wound up seventh and eighth respectively.
Two-time Road America winner Ben Keating earned his first pole position in the GT Daytona class, although the last five minutes of the session were chopped off due to lightning in the area halting the session early.