Sebastian Vettel put Ferrari on top as Formula One returned from the summer break at the legendary Spa circuit.
Lando Norris replaced Fernando Alonso for FP1 at McLaren as the team potentially evaluate the Brit for a 2019 seat.
Max Verstappen logged the opening time of the session on a 1:46.916 using the soft compound tyre.
On the first runs, Lewis Hamilton led the field on the soft tyres with a 1:44.676 as Mercedes introduced a new engine for this weekend. Bottas on supersofts, Raikkonen, Vettel and Verstappen (all on softs) completed the top 5 before the teams handed back a set of tyres to Pirelli.
Ocon in the Racing Point Force India was the quickest of the midfield runners in the first half of the session in front of Hulkenberg, Sainz, Gasly and Perez. On his debut in an official F1 session, Lando Norris ended up P13 following the first attempts.
The second part of FP1 saw the times fall and the order change. Sebastian Vettel took over at the top thanks to a time of a 1:44.358. Max Verstappen, running with a very skinny rear wing, ended up 0.151s slower than the Ferrari driver. Championship leader Lewis Hamilton clocked the 3rd quickest time, with the Finns Raikkonen and Bottas rounding out the top 5 positions. A single flying lap right at the end of the session put Daniel Ricciardo in 6th - the Aussie missed almost all of FP1 due to an issue with the engine in his RB14.
Ocon was the quickest midfield runner in 7th, ahead of Hulkenberg, Perez and Sainz who completed the top 10.
Gasly, Grosjean, Leclerc, Ericsson, Hartley, Stroll, Magnussen, Norris, Sirotkin and Vandoorne filled positions 11-20.
It was almost an incident-free session apart from a spin for Williams’ Sergey Sirotkin at turn 8 – but the Russian continued without any problems.