Red Bull's Daniel Ricciardo was the biggest casualty after he lost control of his Red Bull at Turn 4, took a trip across the gravel, and thudded into the barriers.
Conditions were clearly hard as Bottas, Vettel and Marcus Ericsson all had early spins at different parts on the circuit before Brendon Hartley and Romain Grosjean took trips through the Turn 4 gravel.
"So you saw a lot of drivers going off, it wasn't that easy to stay on track". The impact with the barrier broke the front wing and front left suspension of the vehicle, causing a brief Virtual Safety auto period as it was recovered from the gravel trap and loaded on a trailer to return to the pits. Robert Kubica, making his first F1 appearance in seven years, spun at Turn 13 before Lance Stroll parked his auto in the gravel at Turn Five.
Vettel finished fourth 0.3 seconds slower than the fastest vehicle, while Raikkonen suffered an engine issue and ended sixth.
Home hero Fernando Alonso started the weekend a morale-boosting sixth, behind Raikkonen, with his McLaren displaying a heavily-revised three-pronged nose - one of several conspicuous upgrades around the pit lane.
Team-mate Stoffel Vandoorne was ninth quickest in second practice and positive about the improved handling of the auto, but said McLaren had to wait until qualifying to know if it had taken a real step forward.
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Mercedes also dominated the second session but this time it was Lewis Hamilton who topped the standings with a best time of 1:18.259, once again achieved on the soft compound tyres.
When the virtual safety auto finished Bottas improved twice on a new set of soft tyres and got down to a 1m18.411s before another Turn 10 moment, this time locking up and running deep after encountering traffic.
The Finn's flyer of one minute and 18.148 seconds enabled him to finish nearly of nine-tenths of a second clear of Hamilton with Ferrari's Sebastian Vettel third. Vettel was the fastest supersoft runner but was still a tenth down on the Dutchman. However, the gap between the top three and the rest was clear, with Grosjean's best time some 1.3s off the pace and 0.8s behind Raikkonen. The Ferrari driver also took a trip through the gravel before bringing his auto in for some diagnosis.
That caused a second virtual safety auto and when that ended Bottas improved his benchmark yet again.
In the afternoon session it was Lewis Hamilton's turn to lead the field ending fastest with a time of 1.18.259.
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