Lieb, who shares the #2 Porsche 919 Hybrid with Romain Dumas and Neel Jani, set a best time of 1m41.703s with 18 minutes to go in a session that was extended by 20 minutes due to a lengthy red flag period early on.

Shortly after Nicolas Lapierre caused a full-course yellow as he went into the gravel at Turn 1 in the #36 Signatech Alpine, the session was stopped as race control's messaging system with the teams failed.

At that stage, Marcel Fassler had set the benchmark in the #7 Audi R18 e-tron quattro, although once the session resumed, Lucas di Grassi in the sister #8 Audi soon took control with a succession of hot laps.

By the halfway mark, the Brazilian led the way on a 1m42.326s, and with 30 minutes remaining, Loic Duval lowered the bar to a 1m42.154s.

Porsche ended Audi's reign in P1 a short time after, as Timo Bernhard posted a 1m41.967s in the #1 car, which in turn was soon beaten by Lieb's session-topping effort. Hartley made a late challenge for the top spot, but fell 0.047s short.

Behind the Porsches, Audi occupied third and fourth spots, a last-ditch time of 1m41.903s by Andre Lotterer putting the #7 car clear of the #8, which was fourth with Duval at the wheel.

Toyota's pair of TS050 Hybrids completed the top six, with Sebastien Buemi putting the #5 car fifth, 0.890s off the pace, ahead of Mike Conway in the #6 machine a further second back.

Rebellion Racing's #13 car led the LMP1-L charge in seventh overall, but lapped 6.657s slower than the best of the hybrid machines.

G-Drive, Ferrari top classes

The LMP2 class was topped by the #26 G-Drive Oreca 05-Nissan, as new recruit Alex Brundle posted a best time of 1m50.748s in the closing stages.

That was enough to beat the #44 Manor Oreca by almost seven tenths, while the #42 Strakka Gibson was third quickest, only 0.033s slower.

James Calado meanwhile left it late to set the best time in the GTE Pro class, a 1m58.402s, putting the #51 AF Corse Ferrari 488 two tenths up on the #97 Aston Martin Vantage.

Ford, despite running with the same Balance of Performance as it did at Le Mans, could do no better than fifth and sixth with its pair of GT machines, behind the respective second Aston and Ferrari entries.

In GTE-Am, the #99 Aston Martin Vantage set the pace, with Pedro Lamy setting the pace on a 1m59.949s.

Check out our trackside video highlights...

Practice times:

Cla	#	Drivers	Car	Class	Time	Gap
1	2	Romain Dumas Neel Jani Marc Lieb	Porsche 919 Hybrid	LMP1	1'41.703
2	1	Mark Webber Timo Bernhard Brendon Hartley	Porsche 919 Hybrid	LMP1	1'41.750	0.047
3	7	Andre Lotterer Marcel Fassler	Audi R18	LMP1	1'41.903	0.200
4	8	Lucas di Grassi Loic Duval Oliver Jarvis	Audi R18	LMP1	1'42.154	0.451
5	5	Anthony Davidson Kazuki Nakajima Sébastien Buemi	Toyota TS050 Hybrid	LMP1	1'42.593	0.890
6	6	Stéphane Sarrazin Kamui Kobayashi Mike Conway	Toyota TS050 Hybrid	LMP1	1'43.635	1.932
7	13	Alexandre Imperatori Dominik Kraihamer Matheo Tuscher	Rebellion R-One	LMP1	1'48.360	6.657
8	12	Nick Heidfeld Nicolas Prost Mathias Beche	Rebellion R-One	LMP1	1'48.364	6.661
9	4	Simon Trummer Oliver Webb Pierre Kaffer	CLM P1/01	LMP1	1'48.984	7.281
10	26	Roman Rusinov René Rast Alex Brundle	Oreca 05	LMP2	1'50.748	9.045
11	44	Antonio Pizzonia Matthew Howson Tor Graves	Oreca 05	LMP2	1'51.436	9.733
12	42	Nick Leventis Jonny Kane Lewis Williamson	Gibson 015S	LMP2	1'51.469	9.766
13	31	Pipo Derani Ryan Dalziel Chris Cumming	Ligier JS P2	LMP2	1'51.669	9.966
14	45	Roberto Merhi Richard Bradley Matthew Rao	Oreca 05	LMP2	1'52.333	10.630
15	43	Bruno Senna Ricardo Gonzalez Filipe Albuquerque	Ligier JS P2	LMP2	1'52.471	10.768
16	37	Vitaly Petrov Viktor Shaytar Kirill Ladygin	BR01	LMP2	1'52.647	10.944
17	35	Nelson Panciatici Ho-Pin Tung David Cheng	Alpine A460	LMP2	1'52.825	11.122
18	27	Maurizio Mediani David Markozov Nicolas Minassian	BR01	LMP2	1'52.845	11.142
19	30	Scott Sharp Ed Brown Johannes van Overbeek	Ligier JS P2	LMP2	1'53.983	12.280
20	51	Gianmaria Bruni James Calado	Ferrari 488 GTE	LMGTE PRO	1'58.402	16.699
21	97	Darren Turner Richie Stanaway	Aston Martin Vantage V8	LMGTE PRO	1'58.601	16.898
22	95	Marco Sorensen Nicki Thiim	Aston Martin Vantage V8	LMGTE PRO	1'58.982	17.279
23	71	Sam Bird Davide Rigon	Ferrari 488 GTE	LMGTE PRO	1'59.498	17.795
24	66	Stefan Mücke Olivier Pla	Ford GT	LMGTE PRO	1'59.560	17.857
25	67	Harry Tincknell Andy Priaulx Marino Franchitti	Ford GT	LMGTE PRO	1'59.784	18.081
26	98	Pedro Lamy Paul Dalla Lana Mathias Lauda	Aston Martin Vantage V8	LMGTE AM	1'59.949	18.246
27	77	Richard Lietz Michael Christensen	Porsche 911 RSR (2016)	LMGTE PRO	2'00.483	18.780
28	50	Paolo Ruberti Pierre Ragues Yutaka Yamagishi	Chevrolet Corvette C7-Z06	LMGTE AM	2'00.755	19.052
29	83	François Perrodo Emmanuel Collard Rui Aguas	Ferrari F458 Italia	LMGTE AM	2'00.890	19.187
30	88	David Heinemeier Hansson Patrick Long Khaled Al Qubaisi	Porsche 911 RSR	LMGTE AM	2'01.369	19.666
31	78	Christian Ried Wolf Henzler Joel Camathias	Porsche 911 RSR	LMGTE AM	2'01.487	19.784
32	86	Michael Wainwright Adam Carroll Ben Barker	Porsche 911 RSR	LMGTE AM	2'01.509	19.806
33	36	Nicolas Lapierre Gustavo Menezes Stéphane Richelmi	Alpine A460	LMP2	2'32.739	51.036