Following the fifth yellow flag, at the end of the ninth hour, leader Renger van der Zande in the #01 Chip Ganassi Racing Cadillac V-LMDh sprinted away but Jack Aitken in the #31 Action Express Racing Cadillac got ahead of Richard Westbrook in the #02 Ganassi machine.
But it wasn't long before Westbrook was demoted back to fifth, Mathieu Jaminet in the #6 Porsche 963 and Tom Blomqvist in the Meyer Shank Racing Acura ARX-06 that had previously led before a spin for Helio Castroneves in the seventh hour when trying to retake the advantage.
Blomqvist then blasted past Jaminet down to Turn 1 on the next lap, and kept pushing hard to zap past Aitken, carrying so much momentum out of the Bus Stop chicane that he was able to haul in the Cadillac to grab second.
Blomqvist continued that forward momentum and, on lap 298, he got past van der Zande – who wisely didn’t put up a huge fight on worn tyres – and then he also lost out to Jaminet. Fifteen minutes later, van der Zande was down to fourth behind Aitken.
The sixth yellow followed less than 30 minutes later prompting a rash of stops but, in anticipation of that yellow, Meyer Shank pitted its car and installed Colin Braun, with Aitken and van der Zande also stopping.
Once the yellow flew and the pits opened, Braun pitted again leaving Aitken and van der Zande up front, with Jaminet and Westbrook pitting the #6 Porsche and #02 Cadillac respectively.
Thanks to the yellow, the top seven were now on the same lap and, at the drop of the green, Braun wasted no time in demoting van der Zande and two laps later Jaminet’s Porsche also got around the #01 Caddy.
Fifteen minutes before the completion of the 11th hour, the AXR Cadillac and the #01 Ganassi Cadillac pitted, Alex Sims not taking on new tyres on the AXR car, while Scott Dixon took over the #01 from van der Zande but departed before the pit equipment was detached and incurred a drivethrough penalty.
Next time by, Jaminet stopped, handing the #6 Porsche to Dane Cameron, while Braun went a lap longer. The upshot of all these pitstops was that Sims’s Cadillac led by nine seconds ahead of Braun’s MSR Acura, with Cameron in third.
Just before the end of the 11th hour, Braun moved the MSR Acura back into the lead ahead of Sims. By this time, Cameron was 25s adrift and starting to get pressure from Louis Deletraz in the second Acura, who soon made the move.
Braun was the last of the leaders to stop in the next pit cycle and handed the Acura to 2016 IndyCar champion and defending Daytona 24 Hours winner Simon Pagenaud. When Pagenaud was up to speed, he had a 16.5s lead over Sims’s AXR Caddy, with Deletraz a further 23s down, and Cameron 11s further back.
In the LMP2 class, the leading PR1M car of Alex Quinn, Nicolas Lapierre, Ben Keating and Paul-Loup Chatin endured a long stop just before the halfway mark, allowing Proton Competiton's James Allen into the class lead, 13s clear of the AF Corse ORECA of Nicklas Nielsen.
The Sean Creech Motorsport Ligier of Nico Pino, Joao Barbosa, Lance Willsey and Nolan Siegel continued to lead the LMP3 runners. But there was drama just before half-distance for the MRS GT-Racing Ligier as it caught fire at the rear and caused the race's seventh caution period.
There was trouble for the GTD Pro contending Corvette of Jordan Taylor as the race approached its midpoint when he suddenly slowed with an apparent puncture and had to hobble to the pits, emerging sixth in class. He was soon back in the pits again, however, due to suspected brake damage incurred while limping with the puncture.
Following the latest round of stops, the GTD Pro Heart of Racing Aston Martin led the GT3 class with Ross Gunn at the wheel, while Maxi Gotz was the GTD leader in the Team Korthoff Mercedes ahead of Marvin Kirchhofer’s McLaren.
