Lewis Hamilton set the quickest time as Mercedes seized the early initiative at the French Grand Prix.
The Briton and teammate Valtteri Bottas would trade the top position on several occasions during a flurry of flying laps on the soft compound tyre.
With the current championship leader eventually posting a 1m32.738s to lead the Finn by just 0.069s.
For Ferrari, it was an experimental session as they trialled a new front wing amid other tweaks which they believe will solve the lack of performance this season.
Initial signs were mixed though as Charles Leclerc was pretty competitive in third just three-tenths back of the Mercedes.
Teammate Sebastian Vettel would struggle more however, as problems with understeer left the German a second off the pace in fifth.
Max Verstappen showed strong early pace on the medium tyre in the Red Bull, but would slip eight-tenths back on the softs to split the two Prancing Horses in fourth.
Pierre Gasly would be sixth just ahead of the two McLaren's as the British team looked very competitive throughout the morning to lead the midfield in seventh and eighth.
Renault arrive at their home race with high expectations after a strong weekend in Canada and a raft of upgrades for Paul Ricard.
Initial results were a little disappointing with Daniel Ricciardo ninth and Nico Hulkenberg 12th, but it is likely their performance will increase as they better understand the new parts.
Completing the top 10 would be Alex Albon in the Toro Rosso, the only driver from the two Red Bull-owned squads not to be using the updated Honda engine this weekend.
Racing Point appear quite strong in the early going with Sergio Perez and Lance Stroll 11th and 13th despite setting their best time on the medium tyre.
There were problems at Haas though with Kevin Magnussen a lowly 15th and Romain Grosjean at the bottom of the timesheet having missed much of the session to a water leak.
An interesting dynamic at Williams where Nicholas Latifi got a second Friday morning outing in a row and would narrowly beat Robert Kubica by just 0.025s as speculation grows over whether the F2 championship leader could replace the Pole.
Under hot, sunny skies at Paul Ricard, the main theme of the session was a lack of grip as several drivers spun, including both Red Bulls.
Also, degradation on the soft tyre looks set to be a factor as the fronts in particular grained up through the many long-radius corners.
This should improve as the tracks rubbers in, but with temperatures only rising it will be interesting to see what happens in the long runs in the afternoon.
Full results from Practice 1 can be seen below:
