The championship-leading #2 Porsche of Neel Jani, Marc Lieb and Romain Dumas led the way in first practice for the FIA WEC season finale at Bahrain.
With Jani at the wheel in the early stages, the #2 919 Hybrid produced a laptime of 1m42.107s, 0.343s clear of its nearest rival, the #8 Audi of Loic Duval.
At the start of its final weekend in the series before exiting endurance racing, Audi put its pair of R18 e-tron quattros second and third fastest, Benoit Treluyer lapping 0.408s off the pace of Jani in the #7 car.
The #6 Toyota, which arrives in Bahrain with an outside shot at the drivers' title, was fourth quickest in the hands of Kamui Kobayashi, 0.758s slower than the car it trails by 17 points.
Completing the top six were the #1 Porsche of Timo Bernhard and the #5 Toyota of Sebastien Buemi.
Rebellion, which is taking part in its last weekend in LMP1 before stepping down to race in LMP2 next year, led sole LMP1-L class rival ByKolles by some two seconds.
The LMP2 class was led by the #36 Signatech Alpine, which wrapped up the title last time out at Shanghai, with Nicolas Lapierre establishing a benchmark of 1m50.966s.
Second-quickest was the #45 Manor Oreca of WEC returnee Roberto Merhi, a mere 0.190s slower, followed by the #26 G-Drive car (which has Rene Rast back at the wheel this weekend) driven by Alex Brundle, a further 0.058s behind.
Aston Martin on top in GTE
In GTE-Pro, Aston Martin led the way with a one-two ahead of this weekend's five-way decider.
Darren Turner put the #97 Vantage, which is out of the title race, on top with a 1m58.735 in the car he will share this weekend with Jonathan Adam, with Richie Stanaway absent.
The points-leading #95 car driven by Nicki Thiim was 0.388s back from the sister car, and three tenths up on the #77 Dempsey-Proton Porsche of Richard Lietz.
Ford, which has been hit with a 25kg Balance of Performance weight penalty after winning the last two rounds at Fuji and Shanghai, was only fifth and seventh fastest, with the two AF Corse-run Ferrari 458s taking fourth and sixth.
In GTE-Am, it was the #83 AF Corse Ferrari - which needs to score only one point this weekend to be confirmed as class champion - that led the way courtesy of a 2m01.550s lap by Emmanuel Collard.
The only car that can stop it, the #98 Aston Martin, caused a full-course yellow period after 34 minutes as Paul Dalla Lana's car had to be recovered from the gravel at Turn 1.
First practice results:
|1||2|| Romain Dumas
|Porsche 919 Hybrid||LMP1||1'42.107|
|2||8|| Lucas di Grassi
|3||7|| Andre Lotterer
|4||6|| Stéphane Sarrazin
|Toyota TS050 Hybrid||LMP1||1'42.865||0.758|
|5||1|| Mark Webber
|Porsche 919 Hybrid||LMP1||1'42.955||0.848|
|6||5|| Anthony Davidson
|Toyota TS050 Hybrid||LMP1||1'43.504||1.397|
|7||13|| Alexandre Imperatori
|8||4|| Simon Trummer
|9||36|| Nicolas Lapierre
|10||45|| Roberto Merhi
|11||26|| Rene Rast
|12||43|| Bruno Senna
|Ligier JS P2||LMP2||1'51.581||9.474|
Giedo van der Garde
|Ligier JS P2||LMP2||1'51.631||9.524|
|14||37|| Vitaly Petrov
|15||35|| Paul-Loup Chatin
|16||44|| Richard Bradley
|17||27|| Maurizio Mediani
|18||31|| Pipo Derani
|Ligier JS P2||LMP2||1'52.650||10.543|
|19||97|| Darren Turner
|Aston Martin Vantage V8||LMGTE PRO||1'58.735||16.628|
|20||95|| Marco Sorensen
|Aston Martin Vantage V8||LMGTE PRO||1'59.123||17.016|
|21||77|| Richard Lietz
|Porsche 911 RSR (2016)||LMGTE PRO||1'59.420||17.313|
|22||71|| Sam Bird
|Ferrari 488 GTE||LMGTE PRO||1'59.499||17.392|
|23||67|| Harry Tincknell
|Ford GT||LMGTE PRO||1'59.772||17.665|
|24||51|| Gianmaria Bruni
|Ferrari 488 GTE||LMGTE PRO||1'59.860||17.753|
|25||66|| Stefan Mücke
|Ford GT||LMGTE PRO||2'00.371||18.264|
|26||83|| François Perrodo
|Ferrari F458 Italia||LMGTE AM||2'01.550||19.443|
|27||98|| Pedro Lamy
Paul Dalla Lana
|Aston Martin Vantage V8||LMGTE AM||2'01.552||19.445|
|28||50|| Pierre Ragues
|Chevrolet Corvette C7-Z06||LMGTE AM||2'01.811||19.704|
|29||86|| Michael Wainwright
|Porsche 911 RSR||LMGTE AM||2'02.195||20.088|
|30||88|| David Heinemeier Hansson
Khaled Al Qubaisi
|Porsche 911 RSR||LMGTE AM||2'02.237||20.130|
|31||78|| Christian Ried
|Porsche 911 RSR||LMGTE AM||2'02.496||20.389|