Action Express Racing and Mazda Team Joest traded the lead of Motul Petit Le Mans as night fell, with the former out front with two hours to go.
The No. 5 Mustang Sampling Cadillac DPi-V.R. of Filipe Albuquerque, Mike Conway and Joao Barbosa led the 10-hour race at the halfway point, but lost its advantage early in the sixth hour.
An overtake from Timo Bernhard put the No. 77 Team Joest Mazda RT24-P DPi out front for the first time, ending a Cadillac command that had stretched back to the start of the IMSA WeatherTech SportsCar Championship season finale.
Bernhard’s move on Barbosa into the tight Turn 10a left-hander gave the Mazda a net lead that it would hold for around two hours, until Conway put the Action Express-operated Mustang Sampling car back into the ascendancy.
Toyota LMP1 driver Conway performed a similar move into the same corner on Tristan Nunez midway through hour eight, before pitting shortly afterward.
As things stand, the two Action Express Cadillacs are pitting earliest of the DPi runners, with Mazda keeping its No. 77 car out six laps longer than the leader at the most recent service.
The third-placed entry with two hours remaining was the No. 31 AXR-run Whelen Engineering Cadillac of Felipe Nasr, Eric Curran and Pipo Derani, just over 10 seconds off the tail of the Mazda.
In fourth was the No. 10 Wayne Taylor Racing Cadillac, ahead of the two Team Penske Acura ARX-05 DPis.
The GT Le Mans class order changed around halfway when Dirk Mueller brought out the third and most recent Full Course Yellow just before halfway.
This incident left just one Chip Ganassi Racing Ford GT in the lead battle, with Scott Dixon and then Richard Westbrook taking turns to lead from the Risi Competizione Ferrari 488 GTE.
These two cars switched places in the eighth hour, when Pier Guidi shot past Westbrook to set the pole-sitting Ferrari back out front.
Behind the lead pair was the No. 25 BMW M8 GTE, which is currently holding its position from the two Coca Cola-liveried Porsche 911 RSRs.
At the end of eight hours, the GT Daytona class was led by the No. 96 Turner Motorsport BMW M6 GT3 with Robby Foley at the wheel.
Foley, who shares the car with Bill Auberlen and Dillon Machavern, has been fending off both the No. 29 Montaplast by Land-Motorsport Audi R8 LMS GT3 Evo and the No. 9 Pfaff Motorsports Porsche for the last few stints.