Spanish GP: Valtteri Bottas tops first practice as Lance Stroll crashes
Mercedes driver Valtteri Bottas headed the two Ferraris in a closely matched first practice session at the Spanish Grand Prix.
Bottas, the world championship leader, was 0.115 seconds quicker than Sebastian Vettel, with Charles Leclerc a further 0.106secs behind.
Lewis Hamilton was fourth quickest, complaining that his tyres had not been in suitable shape on his quickest lap.
Practice ended with a crash for Racing Point's Lance Stroll at Turn Nine.
The Canadian brushed the grass on entry to the fast right-hander and speared straight into the wall.
The incident ended the session a minute early.
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Ferrari saved an upgraded engine for the weekend, running an old one on Friday.
Vettel said on Thursday that Ferrari had to start beating Mercedes after seeing the world champions take one-two finishes in all four races so far this season.
The German is already 35 points - more than a clear win - behind Bottas, who is one ahead of Hamilton.
Ferrari have brought forward the engine upgrade by two races in an attempt to finally deliver on what they believe is the potential of their car, in addition to aerodynamic upgrades.
Mercedes also have aerodynamic upgrades, as do most teams in the pit lane, as is traditional at this first European race of the season.
Bottas' morning ended early when he suffered an oil leak which caused what the team said was a "precautionary engine shutdown" and he missed the final 20 minutes of the session while the team investigated.
Hamilton was 0.624secs slower than Bottas, complaining after his quickest lap: "Tyre prep terrible. Rear tyres are done."
Max Verstappen's Red Bull also ran into trouble, his car up on stands in the garage for the last 15 minutes of the session as the team investigated a fluid leak of some kind.
The Dutchman was only 12th fastest, four places behind team-mate Pierre Gasly.
Haas driver Romain Grosjean was best of the rest in fifth, ahead of McLaren's Carlos Sainz and the second Haas of Kevin Magnussen.
Toro Rosso's Daniil Kvyat was ninth, ahead of the Renaults of Nico Hulkenberg and Daniel Ricciardo.
Renault also have an upgraded engine for this weekend, although they have so far been cagey as to whether the works cars are using it.
McLaren said both their cars had the new engine fitted from the start of Friday practice, but Renault said only that their "plan is that all four cars have the new engine for this race weekend".
Official FIA documents said that Ricciardo was using it on Friday but not Hulkenberg.