
Antonio Fuoco set a best time of 1m35.649s at the end of the 90-minute session in the #50 Ferrari 499P LMH, a massive 2.6 seconds up on the sister #51 machine as the track rapidly improved late on.
Best of the rest in third was the #94 Peugeot 9X8, followed by the two works Penske Porsche 963s in fourth and fifth, while home favourite Toyota was sixth and seventh with its two GR010 HYBRIDs.
Despite the looming threat of Typhoon Yun-yeung, Friday morning's 90-minute session started on schedule at 11am local time in wet conditions and passed largely without incident.
Almost every Hypercar class manufacturer enjoyed a stint at the top of the times, as the track steadily dried out.
Ferrari took command of the times with a little over 30 minutes to go as James Calado went quickest in the #51 car, with team-mate Antonio Giovinazzi becoming the first driver to breach the 1m40s mark when he set a 1m39.198s with 22 minutes left on the clock.
Fuoco then traded the top time with Giovinazzi as he took over at the wheel of the #50 Ferrari, with Porsche man Michael Christensen briefly snatching the advantage before Fuoco went faster again, posting a 1m37.616s and then a 1m35.649s after switching to slick tyres.
Giovinazzi set the best time in the #51 car of 1m38.258s on wets, just over four tenths up on late improver Gustavo Menezes in the #94 Peugeot.
Christensen's time was eclipsed late on by his opposite number in the sister #6 Porsche, Laurens Vanthoor, who posted a 1m38.729s to go fourth-fastest.
Mike Conway set the best time for Toyota of 1m39.251s in the #7 car, four hundredths quicker than Brendon Hartley in the #8 car in a subdued opening session for the Japanese manufacturer.
Completing the top 10 were the second of the Peugeots, the #93 car in which Paul di Resta set the best time, the solo Cadillac V-Series.R of Alex Lynn and the Proton Competition customer Porsche of Harry Tincknell.
The JOTA Porsche enjoyed a lengthy spell at the top of the times in the opening half of the session when conditions were at their worst, but ended up 11th in the Hypercar class and slower than the team's LMP2 car, which topped that class.
Oliver Rasmussen put in a late flyer of 1m40.781s aboard the #28 ORECA 07 to take the top spot in LMP2, almost two seconds up on nearest rival Filip Ugran in the #9 Prema machine.
United Autosports was third in class courtesy of a late effort from Ben Hanley - standing in for Tom Blomqvist this weekend - in the #23 entry.
Topping the times by an even wider margin in GTE Am was the #77 Dempsey Proton Porsche 911 RSR-19 of Mikkel Pedersen on a 1m43.538s.
That was almost four seconds up on Davide Rigon, who went second-fastest in the #54 AF Corse Ferrari 488 GTE.
A sole full-course yellow was called at the one-hour mark, but this was purely procedural rather than in response to any accident.
FP2 is scheduled to begin at 3.30pm local time, but more rain is forecast for later in the day, casting doubt on whether the session will run as planned.
Fuji WEC - First practice results:
| Pos. | No. | Drivers | Car | Class | time | gap | 
|---|---|---|---|---|---|---|
| 1 | 50 | 
  Antonio Fuoco  Miguel Molina  Nicklas Nielsen | 
Ferrari 499P | HYPERCAR | 1'35.649 | |
| 2 | 51 | 
  Alessandro Pier Guidi  James Calado  Antonio Giovinazzi | 
Ferrari 499P | HYPERCAR | 1'38.258 | 2.609 | 
| 3 | 94 | 
  Loïc Duval  Gustavo Menezes  Stoffel Vandoorne | 
Peugeot 9X8 | HYPERCAR | 1'38.693 | 3.044 | 
| 4 | 6 | 
  Kevin Estre  Andre Lotterer  Laurens Vanthoor | 
Porsche 963 | HYPERCAR | 1'38.729 | 3.080 | 
| 5 | 5 | 
  Dane Cameron  Michael Christensen  Frédéric Makowiecki | 
Porsche 963 | HYPERCAR | 1'38.876 | 3.227 | 
| 6 | 7 | 
  Mike Conway  Kamui Kobayashi  Jose Maria Lopez | 
Toyota GR010 - Hybrid | HYPERCAR | 1'39.251 | 3.602 | 
| 7 | 8 | 
  Sebastien Buemi  Brendon Hartley  Ryo Hirakawa | 
Toyota GR010 - Hybrid | HYPERCAR | 1'39.291 | 3.642 | 
| 8 | 93 | 
  Paul di Resta  Mikkel Jensen  Jean-Eric Vergne | 
Peugeot 9X8 | HYPERCAR | 1'39.309 | 3.660 | 
| 9 | 2 | 
  Earl Bamber  Alex Lynn  Richard Westbrook | 
Cadillac V-Series.R | HYPERCAR | 1'39.584 | 3.935 | 
| 10 | 99 | 
  Neel Jani  Gianmaria Bruni  Harry Tincknell | 
Porsche 963 | HYPERCAR | 1'40.085 | 4.436 | 
| 11 | 28 | 
  David Heinemeier Hansson  Pietro Fittipaldi  Oliver Rasmussen | 
Oreca 07 | LMP2 | 1'40.781 | 5.132 | 
| 12 | 38 | 
  Antonio Felix da Costa  Will Stevens  Ye Yifei | 
Porsche 963 | HYPERCAR | 1'40.953 | 5.304 | 
| 13 | 4 | 
  Esteban Guerrieri  Tristan Vautier | 
Vanwall Vandervell 680 | HYPERCAR | 1'41.483 | 5.834 | 
| 14 | 9 | 
  Filip Ugran  Bent Viscaal  Juan Manuel Correa | 
Oreca 07 | LMP2 | 1'42.661 | 7.012 | 
| 15 | 23 | 
  Josh Pierson  Ben Hanley  Oliver Jarvis | 
Oreca 07 | LMP2 | 1'42.924 | 7.275 | 
| 16 | 10 | 
  Ryan Cullen  Matthias Kaiser  Gabriel Aubry | 
Oreca 07 | LMP2 | 1'42.984 | 7.335 | 
| 17 | 34 | 
  Jakub Smiechowski  Fabio Scherer  Albert Costa | 
Oreca 07 | LMP2 | 1'43.204 | 7.555 | 
| 18 | 36 | 
  Matthieu Vaxivière  Julien Canal  Charles Milesi | 
Oreca 07 | LMP2 | 1'43.218 | 7.569 | 
| 19 | 22 | 
  Frederick Lubin  Philip Hanson  Filipe Albuquerque | 
Oreca 07 | LMP2 | 1'43.230 | 7.581 | 
| 20 | 31 | 
  Sean Gelael  Ferdinand Habsburg  Robin Frijns | 
Oreca 07 | LMP2 | 1'43.403 | 7.754 | 
| 21 | 41 | 
  Rui Andrade  Robert Kubica  Louis Deletraz | 
Oreca 07 | LMP2 | 1'43.490 | 7.841 | 
| 22 | 77 | 
  Christian Ried  Mikkel Pedersen  Julien Andlauer | 
Porsche 911 RSR - 19 | LMGTE AM | 1'43.538 | 7.889 | 
| 23 | 63 | 
  Doriane Pin  Andrea Caldarelli  Daniil Kvyat | 
Oreca 07 | LMP2 | 1'44.139 | 8.490 | 
| 24 | 35 | 
  André Negrão  Memo Rojas  Olli Caldwell | 
Oreca 07 | LMP2 | 1'44.816 | 9.167 | 
| 25 | 54 | 
  Thomas Flohr  Francesco Castellacci  Davide Rigon | 
Ferrari 488 GTE EVO | LMGTE AM | 1'47.198 | 11.549 | 
| 26 | 56 | 
  PJ Hyett  Gunnar Jeannette  Matteo Cairoli | 
Porsche 911 RSR - 19 | LMGTE AM | 1'47.230 | 11.581 | 
| 27 | 83 | 
  Luis Perez Companc  Lilou Wadoux  Alessio Rovera | 
Ferrari 488 GTE EVO | LMGTE AM | 1'47.250 | 11.601 | 
| 28 | 777 | 
  Satoshi Hoshino  Casper Stevenson  Tomonobu Fujii | 
Aston Martin Vantage AMR | LMGTE AM | 1'47.493 | 11.844 | 
| 29 | 98 | 
  Ian James  Daniel Mancinelli  Alex Riberas | 
Aston Martin Vantage AMR | LMGTE AM | 1'47.913 | 12.264 | 
| 30 | 21 | 
  Hiroshi Koizumi  Simon Mann  Kei Cozzolino | 
Ferrari 488 GTE EVO | LMGTE AM | 1'48.414 | 12.765 | 
| 31 | 60 | 
  Claudio Schiavoni  Matteo Cressoni  Alessio Picariello | 
Porsche 911 RSR - 19 | LMGTE AM | 1'49.060 | 13.411 | 
| 32 | 86 | 
  Michael Wainwright  Riccardo Pera  Ben Barker | 
Porsche 911 RSR - 19 | LMGTE AM | 1'49.199 | 13.550 | 
| 33 | 85 | 
  Sarah Bovy  Michelle Gatting  Rahel Frey | 
Porsche 911 RSR - 19 | LMGTE AM | 1'49.455 | 13.806 | 
| 34 | 57 | 
  Takeshi Kimura  Scott Huffaker  Ritomo Miyata | 
Ferrari 488 GTE EVO | LMGTE AM | 1'49.706 | 14.057 | 
| 35 | 33 | 
  Ben Keating  Nicolas Varrone  Nicky Catsburg | 
Chevrolet Corvette C8.R | LMGTE AM | 1'50.043 | 14.394 | 
| 36 | 25 | 
  Ahmad Al Harthy  Michael Dinan  Charlie Eastwood | 
Aston Martin Vantage AMR | LMGTE AM | 1'53.388 | 17.739 | 
 Antonio Fuoco
 Miguel Molina
 Nicklas Nielsen
 James Calado
 Loïc Duval
 Gustavo Menezes
 Stoffel Vandoorne
 Andre Lotterer
 Kamui Kobayashi
 Jose Maria Lopez
 Sebastien Buemi
 Brendon Hartley
 Pietro Fittipaldi
 Antonio Felix da Costa
 Ye Yifei
 Filip Ugran
 Bent Viscaal
 Juan Manuel Correa
 Ryan Cullen
 Jakub Smiechowski
 Sean Gelael
 Ferdinand Habsburg
 Daniil Kvyat
 Memo Rojas