Max Verstappen topped the time-sheets ahead of team-mate Daniel Ricciardo as the Red Bull duo set the pace in a rain-affected first practice session at the Malaysian Grand Prix.
World championship leader Lewis Hamilton was in sixth with nearest title rival Sebastian Vettel a place ahead of him for Ferrari.
A heavy downpour led to the session being delayed by 30 minutes and when it got under way there was very little on-track action as drivers waited for the circuit to dry.
With no further rain, all the action came in the final hour of the 90-minute session, Verstappen posting the fastest time with an effort of 1min 48.962seconds.
His team-mate Ricciardo was some way back in second while Fernando Alonso's McLaren was third, finishing the session above the Ferrari pair of Kimi Raikkonen and Vettel.
Hamilton was sixth ahead of the sister Mercedes of Valtteri Bottas with Lance Stroll eighth for Williams and Pierre Gasly, in his first race weekend as a fully-fledged Toro Rosso driver, ninth.
Sergey Sirotkin, running in free practice in place of Nico Hulkenberg, recovered from a spin to round out the top 10 for Renault.
His team-mate Jolyon Palmer was 11th with the second McLaren of Stoffel Vandoorne 12th and Force India's Esteban Ocon 13th.
Sean Gelael replaced Carlos Sainz for FP1 and took 14th for Toro Rosso, the Indonesian followed by Sergio Perez's Force India and Ferrari protege Charles Leclerc - who was in for Marcus Ericsson at Sauber.
Pascal Wehrlein spun towards the end of the session and the German could only manage the 17th fastest lap as the times tumbled on a drying track
The Haas pair of Romain Grosjean and test driver Antonio Giovinazzi were only kept off the bottom of the timing sheet by the Williams of Felipe Massa as a problem with hydraulics severely restricted his running.