Porsche's World Endurance champion Neel Jani edged Action Express Racing's Cadillacs to take pole position for the Sebring 12 Hours, as Christian Fittipaldi ran out of fuel on his final lap.
Pipo Derani was apparently the first driver heading for a sub-1min49sec lap but ducked into the pits with a boost issue, so Rebellion Racing's Jani took up the fight to lower the track record of 1m51.217s.
He blew that out of the water with a 1min48.178s, ahead of the Action Express Racing Cadillac DPi-V.Rs of Christian Fittipaldi on 1m48.273s, and Dane Cameron on 1m48.314s.
Jose Gutierrez was fourth in the #52 PR1/Mathiasen Motorsport Ligier, with Brendon Hartley fifth in the #22 ESM Nissan-Ligier and Ricky Taylor a surprising sixth in the Wayne Taylor Racing Cadillac.
Seventh went to the JDC/Miller machine of Stephen Simpson, Jonathan Bomarito led the Mazda charge in eighth - Mazda's first lap under 1min50sec this weekend - with Renger Van der Zande ninth in Visit Florida Racing's Riley XXX.
Dirk Muller set the early pace in GTLM, clocking a 1min56.175 in the #66 Ford GT, as team-mate Stefan Mucke in the #68 car and the Porsche 911 RSRs of Kevin Estre and Dirk Werner tried to shave his advantage.
But it was the #67 Ford of ex-IndyCar ace Ryan Briscoe that was first car under 1m56s, setting a 1m55.939 and claiming pole by almost a quarter of a second.
Tommy Milner then put in a big effort to take third in the #4 Corvette C7.R, just 0.3sec off Briscoe's best, and Antonio Garcia in the #3 entry was just a tenth slower, albeit with Estre's #912 Porsche between them.
Mucke claimed sixth, just ahead of Werner's Porsche, with Nick Catsburg and Alexander Sims in eighth and ninth for RLL BMW.
Giancarlo Fisichella's Risi Competizione Ferrari 488 was 10th and last, 1.5sec off Briscoe's pole-winning time.
GT Daytona honours went to Tristan Vautier in the SunEnergy1 Racing Mercedes AMG GT3, while Gustavo Yacaman claimed pole in the Prototype Challenge class by 0.069s for BAR1 Motorsports, ahead of James French in the Performance Tech Motorsports entry.