It was the #8 Toyota GR010 HYBRID of Sebastien Buemi that held the advantage over the #51 Ferrari of James Calado at the end of a first hour of action at the Circuit de la Sarthe interrupted by a safety car period following a crash for the Action Express Racing-entered Cadillac.
Jack Aitken appeared to simply lose control of the third-string #311 V-Series.R exiting the first chicane, suffering significant front-left damage, although he was able to wrestle the car back to the pits.
At the head of the field, the two Toyotas of Buemi and Mike Conway were both able to pick off Calado's Ferrari to move into second and third places, and Buemi was soon challenging the pole-sitting #50 499P of Nicklas Nielsen for the lead.
Buemi made the pass on Nielsen just before Indianapolis on the opening lap before the race was neutralised for Aitken's crash.
The first-ever drop back procedure was performed, with numerous LMP2 and GTE Am runners - as well as the customer Jota Porsche 963 - all took the chance to make early pitstops.
When the race resumed, Buemi quickly gapped Nielsen, despite having complained about struggling with his brake regen under the safety car, while Conway was able to pick off the Danish driver for second, again at Indianapolis.
But Conway in the #7 Toyota was soon coming under pressure from both Ferraris, and Nielsen was able to ease his way back into second heading into Mulsanne corner after 53 minutes.
Nielsen dived into the pits at the end of that lap for his first stop, temporarily putting Conway back into second before he was passed by the sister Ferrari of Calado at the first chicane.
At the end of the first hour, Buemi was 4.6s ahead of Calado, with Conway a further 1.4s back in third.
Felipe Nasr was fourth in the best of the Porsches, although the Brazilian picked up a warning for making contact with Buemi's Toyota at the very first corner.
The Brazilian's team-mates Laurens Vanthoor and Michael Christensen ran fifth and sixth ahead of the Chip Ganassi run-Cadillac of Earl Bamber and Peugeot's pair of 9X8s, Paul di Resta leading Nico Muller.
One of the two Glickenhaus 007 LMHs, the #708 car, went a lap down in the early stages after a suffering an oil leak before the race even started.
In LMP2, poleman Paul-Loup Chatin maintained the lead at the wheel of his IDEC Sport ORECA.
Robert Kubica moved up from third to second in the best of the WRT cars, while Reshad de Gerus was briefly third in his COOL Racing entry before pitting just before the end of the first hour.
That promoted Pietro Fittipaldi, who had started second in the Jota ORECA, back up to third.
The #63 Prema car of Daniil Kvyat had held second at the safety car restart, but dropped to the rear of the field after being summoned to the pits to fix a tail light.
In GTE, the pole-winning Corvette Racing car of Nicky Catsburg was among the majority of cars to pit under the safety car.
Among those to stay out was the #54 AF Corse Ferrari 488 GTE of Davide Rigon, who held the advantage at the one-hour mark over the AO Racing Porsche 911 RSR 19 of Matteo Cairoli.
The Garage 56 Chevrolet Camaro ZL1 NASCAR Cup car, started by Mike Rockenfeller, ran 35th overall, ahead of the entire GTE Am field.
