Dumas posted a 3m28.900s at the wheel of the #708 Glickenhaus 007 LMH to beat the best of the Toyota GR010 Hybrids, the #8 machine of Brendon Hartley, by 0.348 seconds.
The best time in the two-hour night session was around 1.7s slower than the time Kamui Kobayashi set in the #7 Toyota in first qualifying.
Mike Conway put the #7 car third in the order with a best effort of 3m29.748s, exactly half a second down on the sister Toyota.
Glickenhaus' #709 entry was fourth-fastest in the hands of Ryan Briscoe, albeit 2.5s down on Dumas' benchmark, followed by the solo Alpine A480-Gibson LMP1 driven by Matthieu Vaxiviere.
LMP2 was topped by Rene Rast at the wheel of the best of the three WRT-run Oreca 07-Gibsons.
Rast posted a 3m33.119s to eclipse the early benchmark set by United Autosports man Filipe Albuquerque to the tune of a little over two tenths.
IMSA WeatherTech SportsCar Championship star Ricky Taylor was third-fastest in the Cool Racing Oreca, ahead of Robert Kubica in the Prema car and Richard Mille Racing's Charles Milesi.
Williams Formula 1 reserve Jack Aitken was sixth-fastest for Algarve Pro Racing and best of the Pro/Am runners.
Corvette Racing led the way in the GTE Pro ranks as Nicky Catsburg set a best effort of 3m53.492s early on in the quicker of the American marque's pair of C8.Rs, the #63 car.
Next up was the best of the factory Porsche 911 RSR-19s, the #91 example of Frederic Makowiecki, with the #64 Corvette of Tommy Milner a mere three hundredths further back in third.
The quickest Ferrari 488 GTE Evo was the privateer Riley Motorsports entry in fourth with Felipe Fraga at the wheel, ahead of the #92 Porsche of Kevin Estre and the two works AF Corse-entered Ferraris.
Danish racer Mikkel Pedersen set the time to beat in the GTE Am ranks at the wheel of the Team Project 1 Porsche.
Two cars involved in earlier accidents did not set a time during the session, the #45 Algarve Pro Racing that had earlier been crashed by Steven Thomas and the #93 Proton Competition Porsche in which Michael Fassbender suffered a shunt.
In a relatively incident-free session, Inter Europol Competition's #43 entry stopped along the start/finish straight with a suspension problem, while the #21 AF Corse Ferrari of Christoph Ulrich needed rescuing from the gravel following an off at Arnage.
| Cla | Nº | Driver | Car / Engine | Time | Gap |
| 1 | 708 | Olivier Pla Romain Dumas Pipo Derani | Glickenhaus/Pipo | 3'28.900 | |
| 2 | 7 | Mike Conway Kamui Kobayashi José María López | Toyota | 3'29.164 | 0.264 |
| 3 | 8 | Sébastien Buemi Brendon Hartley Ryo Hirakawa | Toyota | 3'29.248 | 0.348 |
| 4 | 709 | Ryan Briscoe R.Westbrook Franck Mailleux | Glickenhaus/Pipo | 3'31.440 | 2.540 |
| 5 | 36 | André Negrão Nicolas Lapierre M.Vaxivière | Alpine/Gibson | 3'32.592 | 3.692 |
| 6 | 31 | Sean Gelael Robin Frijns René Rast | ORECA/Gibson | 3'33.119 | 4.219 |
| 7 | 22 | Phil Hanson F.Albuquerque Will Owen | ORECA/Gibson | 3'33.382 | 4.482 |
| 8 | 32 | Rolf Ineichen Mirko Bortolotti Dries Vanthoor | ORECA/Gibson | 3'33.399 | 4.499 |
| 9 | 37 | Yifei Ye Ricky Taylor Niklas Krütten | ORECA/Gibson | 3'33.473 | 4.573 |
| 10 | 9 | Robert Kubica Louis Delétraz Lorenzo Colombo | ORECA/Gibson | 3'33.559 | 4.659 |
| 11 | 41 | Rui Andrade F.Habsburg Norman Nato | ORECA/Gibson | 3'33.641 | 4.741 |
| 12 | 1 | Lilou Wadoux Sébastien Ogier Charles Milesi | ORECA/Gibson | 3'33.692 | 4.792 |
| 13 | 47 | Sophia Flörsch John Falb Jack Aitken | ORECA/Gibson | 3'33.785 | 4.885 |
| 14 | 48 | Paul Lafargue Paul-Loup Chatin Patrick Pilet | ORECA/Gibson | 3'34.115 | 5.215 |
| 15 | 13 | P.Cimadomo Mathias Beche T.van der Helm | ORECA/Gibson | 3'34.270 | 5.370 |
| 16 | 24 | Rodrigo Sales Matthew Bell Ben Hanley | ORECA/Gibson | 3'34.589 | 5.689 |
| 17 | 5 | Dane Cameron Emmanuel Collard Felipe Nasr | ORECA/Gibson | 3'34.645 | 5.745 |
| 18 | 38 | Roberto González A.F.da Costa Will Stevens | ORECA/Gibson | 3'34.773 | 5.873 |
| 19 | 43 | David H.Hansson Fabio Scherer P.Fittipaldi | ORECA/Gibson | 3'34.793 | 5.893 |
| 20 | 44 | Miro Konopka Bent Viscaal Tristan Vautier | ORECA/Gibson | 3'34.804 | 5.904 |
| 21 | 34 | J.Smiechowski Alex Brundle E.Gutiérrez | ORECA/Gibson | 3'34.957 | 6.057 |
| 22 | 65 | Julien Canal Nicolas Jamin Job van Uitert | ORECA/Gibson | 3'34.971 | 6.071 |
| 23 | 3 | Laurents Hörr Jean Glorieux A.Cougnaud | ORECA/Gibson | 3'35.133 | 6.233 |
| 24 | 83 | François Perrodo Nicklas Nielsen Alessio Rovera | ORECA/Gibson | 3'35.313 | 6.413 |
| 25 | 28 | Oliver Rasmussen Ed Jones J.Aberdein | ORECA/Gibson | 3'35.314 | 6.414 |
| 26 | 23 | Alex Lynn Oliver Jarvis Josh Pierson | ORECA/Gibson | 3'35.362 | 6.462 |
| 27 | 30 | Richard Bradley Memo Rojas Reshad De Gerus | ORECA/Gibson | 3'35.383 | 6.483 |
| 28 | 10 | Nico Müller Ryan Cullen S.Bourdais | ORECA/Gibson | 3'35.711 | 6.811 |
| 29 | 35 | J-B.Lahaye Matthieu Lahaye François Heriau | ORECA/Gibson | 3'37.960 | 9.060 |
| 30 | 39 | Eric Trouillet Sebastien Page David Droux | ORECA/Gibson | 3'39.269 | 10.369 |
| 31 | 27 | C.Crespo Michael Jensen Steven Palette | Ligier/Gibson | 3'40.964 | 12.064 |
| 32 | 63 | Antonio García Jordan Taylor Nicky Catsburg | Chevrolet | 3'53.492 | 24.592 |
| 33 | 91 | Gianmaria Bruni Richard Lietz F.Makowiecki | Porsche | 3'53.669 | 24.769 |
| 34 | 64 | Nick Tandy Tommy Milner Alexander Sims | Chevrolet | 3'53.699 | 24.799 |
| 35 | 74 | Felipe Fraga Sam Bird S.van Gisbergen | Ferrari | 3'54.019 | 25.119 |
| 36 | 92 | M.Christensen Kévin Estre Laurens Vanthoor | Porsche | 3'54.158 | 25.258 |
| 37 | 52 | Miguel Molina Antonio Fuoco Davide Rigon | Ferrari | 3'54.925 | 26.025 |
| 38 | 51 | A.P.Guidi James Calado Daniel Serra | Ferrari | 3'55.143 | 26.243 |
| 39 | 46 | Matteo Cairoli M.O.Pedersen Niki Leutwiler | Porsche | 3'55.629 | 26.729 |
| 40 | 88 | Fred Poordad Maxwell Root Jan Heylen | Porsche | 3'55.729 | 26.829 |
| 41 | 98 | Paul Dalla Lana Nicki Thiim David Pittard | Aston Martin | 3'55.941 | 27.041 |
| 42 | 85 | Rahel Frey Michelle Gatting Sarah Bovy | Ferrari | 3'55.999 | 27.099 |
| 43 | 777 | Satoshi Hoshino Tomonobu Fujii Charlie Fagg | Aston Martin | 3'56.035 | 27.135 |
| 44 | 54 | Thomas Flohr F.Castellacci Nick Cassidy | Ferrari | 3'56.108 | 27.208 |
| 45 | 56 | Brendan Iribe Ollie Millroy Ben Barnicoat | Porsche | 3'56.151 | 27.251 |
| 46 | 77 | Christian Ried Seb Priaulx Harry Tincknell | Porsche | 3'56.257 | 27.357 |
| 47 | 60 | C.Schiavoni A.Balzan R.Giammaria | Ferrari | 3'56.470 | 27.570 |
| 48 | 57 | Takeshi Kimura Mikkel Jensen F.Schandorff | Ferrari | 3'56.505 | 27.605 |
| 49 | 99 | Andrew Haryanto A.Picariello Martin Rump | Porsche | 3'56.536 | 27.636 |
| 50 | 80 | Matteo Cressoni G.Fisichella Richard Heistand | Ferrari | 3'56.560 | 27.660 |
| 51 | 33 | Ben Keating H.Chaves Jr. Marco Sørensen | Aston Martin | 3'56.637 | 27.737 |
| 52 | 21 | Simon Mann Christoph Ulrich Toni Vilander | Ferrari | 3'56.679 | 27.779 |
| 53 | 79 | Cooper MacNeil Julien Andlauer Thomas Merrill | Porsche | 3'56.780 | 27.880 |
| 54 | 75 | Pierre Ehret Christian Hook Nicolás Varrone | Ferrari | 3'56.935 | 28.035 |
| 55 | 55 | Duncan Cameron Matt Griffin David Perel | Ferrari | 3'57.165 | 28.265 |
| 56 | 71 | Franck Dezoteux Pierre Ragues Gabriel Aubry | Ferrari | 3'57.456 | 28.556 |
| 57 | 86 | Mike Wainwright Ben Barker Riccardo Pera | Porsche | 3'57.640 | 28.740 |
| 58 | 61 | Louis Prette Jr. Conrad Grunewald Vincent Abril | Ferrari | 3'57.652 | 28.752 |
| 59 | 59 | Alexander West Côme Ledogar Marvin Klein | Ferrari | 3'57.961 | 29.061 |
| 60 | 66 | R.van der Zande Mark Kvamme Jason Hart | Ferrari | 4'00.566 | 31.666 |
| 61 | 45 | Steven Thomas James Allen Rene Binder | ORECA/Gibson | - | - |
| 62 | 93 | M.Fassbender Matt Campbell Z.Robichon | Porsche | - | - |
