Sainz leads Ferrari 1-2 in FP1 as F1 returns to action at Spa
Sainz was just 0.069s faster than Ferrari teammate Charles Leclerc, while championship leader Max Verstappen ended up third-quickest, 0.217s down in his Red Bull.
Verstappen holds an 80-point lead over title rival Leclerc but the pair are among six drivers who will take engine-related grid penalties for Sunday’s grand prix.
McLaren’s Lando Norris, Alfa Romeo’s Valtteri Bottas, Alpine’s Esteban Ocon and Haas driver Mick Schumacher will also be hit with penalties for exceeding their power unit allocations.
FP1 was interrupted by a lengthy red flag when Kevin Magnussen suffered an electrical problem, causing his Haas to grind to a halt at the exit of La Source with just over 20 minutes remaining.
The session resumed with 10 minutes left on the clock but nobody was able to improve when a late downpour of rain left the circuit soaked.
George Russell was the fastest Mercedes driver in fourth, 0.858s off the pace, ahead of Aston Martin’s Lance Stroll and Alex Albon, who put his Williams sixth.
Daniel Ricciardo, whose impending split from McLaren was confirmed on Thursday, was seventh-quickest, with Yuki Tsunoda, Lewis Hamilton and Sergio Perez completing the rest of the top-10 order for AlphaTauri, Mercedes and Red Bull respectively.
A second hour of practice will take place at 5pm local time (4pm UK).
Full results from opening practice at the Belgian Grand Prix.