A drizzle at the beginning of the 15th hour quickly turned into a downpour more than an hour earlier than anticipated, sending virtually the entire field to pit road and scrambling the running order in the Rolex 24.
Felipe Nasr stretched his lead in the No.31 Whelen’s Cadillac, helped by a bit of pit strategy. While his three lead-lap competitors pitted for slicks earlier in the hour, Nasr came in two laps later and went to rain tires. When the downpour began moments later, the No.10 of Fernando Alonso, No.7 of Ricky Taylor and No.6 of Dane Cameron all needed an extra stop for the treaded tires, Nasr boosted his lead to more than 90 seconds – an advantage he lost due to caution later in the hour
Rubens Barrichello was running fifth, two laps down, when he went off in the chicane, damaging bodywork and losing seven laps with a trip to the garage in the No.85 JDC-Miller Motorsports Cadillac.
Elsewhere, Sebastien Bourdais went straight off in the International Horseshoe in the No.66 Ford GT, falling from second to fifth in GTLM.
Porsches ran 1-2 in GTLM prior to the rain, with the No.62 of James Calado taking advantage of the conditions to take the class lead.
The No.18 DragonSpeed ORECA – running second in LMP2 – encountered problems when Ryan Cullen had problems restarting on pit road midway through the hour. Once underway, Cullen quickly returned, with a damaged nose and missing the tail after an incident in Turn 6.
Debris from the Cullen incident brought out the 10th full-course caution. He lost four laps, but retained second in the four-car class.
Meanwhile, the incident involving the No.55 Mazda of Olivier Pla during the 14th hour was traced to the car suddenly losing power in the infield and being punched from behind. The damage cost the team 40 laps, falling from a lead-lap fifth to a distant ninth.
The No.31 of Eric Curran and No.7 of Ricky Taylor both changed noses under the caution, helping Fernando Alonso take the lead in the No.10.
The green flag returned with three minutes remaining in the hour. With nine hours left on the clock, Fernando Alonso leads, the No.81 DragonSpeed of Ben Hanley sits on top in LMP2; the No.762 Ferrari of James Calado in GTLM; and the No.14 Lexus of Nick Cassidy in GTD.