The no17 BR1 was the quicker of the two Russian cars with Sergey Sirotkin setting a 1m56.264 lap, 1.972 ahead of WEC debutant Stoffel Vandoorne in the no11 SMP run car.
The two Toyotas were third and fourth quickest with the no8 TS050-hybrid of Sebastien Buemi on a 1m58.742 lap, 2.478s behind Sirotkin.
There was a dead heat at the top of the LMGTE Pro category with Max Martin posting a 2m15.290 in the no97 Aston Martin Vantage, with Harry Tincknell equalling the Belgian drivers time to the thousandth of a second in the no67 Ford GT in the last few minutes of the 90-minute session.
The no82 BMW Team MTEK M8 was third quickest ahead of the no66 Ford GT. The two Championship leading Porsches were seventh and eighth fastest in the first session.
In the LMP2 class, championship leaders Signatech Alpine Matmut head the category as Nico Lapierre sets 2m03.441s, 0.3s ahead of Jean-Eric Vergne’s 2m03.677s lap in the returning no26 G-Drive Racing Aurus 01-Gibson. Third in LMP2 is the Racing Team Nederland Dallara which just heads the Dragonspeed Oreca in fourth
The no86 Gulf Racing Porsche headed the LMGTE Am category, with Ben Barker setting a 2m17.068s lap. Second in LMGTE Am is the title chasing Spirit of Race Ferrari as Giancarlo Fisichella sets a best of 2m17.316s lap. Placing in third was the Dempsey-Proton Racing Porsche 911 RSR as Matt Campbell quickest lap of 2m17.579s for German team.
CLICK HERE for the result from Free Practice 1 at Spa-Francorchamps.
Second Free Practice scheduled to begin at 16.25 local time