Oliver Gavin led an extremely competitive 50th Rolex for the Spirit of Daytona team as the race passed the quarter-distance mark.
After six hours of racing, 11 cars remained on the lead lap, with Gavin holding a narrow advantage over Alex Gurney of GAINSCO/Bob Stallings Racing.
The #01 Ganassi car, #6 Michael Shank Racing entry and #5 Action Express car were also close to the front as the seventh hour began, while the sister Ganassi and MSR machines, and the Starworks crews had also taken turns at the forefront as the race headed into darkness.
The only top-class entries to have dropped out of contention so far are SunTrust Racing's Corvette, which was retired with engine issues after just 14 laps of racing, and the Doran Dallara-Ford, which has lost seven laps receiving attention to mechanical problems.