Red Bull's Daniel Ricciardo pipped Ferrari's Sebastian Vettel in first practice at the Hungarian Grand Prix.
The Australian was just 0.079 seconds quicker than Vettel but was running on a harder tyre than the German.
Ricciardo's team-mate Max Verstappen was third quickest as only 0.088secs separated the fastest three cars.
Ferrari's Kimi Raikkonen was fourth, 0.335secs off the pace, and ahead of Mercedes' Lewis Hamilton, who had a big spin at Turn Five.
The world championship leader was not the only driver to lose control on the twisty and challenging Hungaroring's dusty track surface.
Sauber's Marcus Ericsson had two spins - one at the final corner early in the session and a high-speed one at the uphill kink of Turn Five, in which he narrowly escaped a sizeable impact with the barriers.
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Verstappen also had a spin, at Turn One, and the other Sauber driver in the session, Antonio Giovinazzi, who was driving Charles Leclerc's car, suffered a major lock-up early in the session. Toro Rosso's Brendon Hartley spun at the final corner right at the end of the session.
Mercedes are expecting a difficult weekend on a track that they believe does not suit their car, and the first indications are that Ferrari and Red Bull do have a small advantage.
Behind the top three, with Mercedes' Valtteri Bottas in sixth, Haas driver Romain Grosjean was best of the rest, jumping ahead of Renault's Nico Hulkenberg at the end of the session.
Hulkenberg did not run for the last half-hour after stopping out on track with an engine shutdown.
The German's team-mate Carlos Sainz was next, ahead of Haas' Kevin Magnussen, Toro Rosso's Pierre Gasly and McLaren's Fernando Alonso.