Sebastian Vettel set the pace in first practice for the Japanese Grand Prix as he got the better of title rival Lewis Hamilton.
With the threat of rain lingering over the session, everyone went out early to put together a run of laps before the downpour arrived, while a red flag also prevented valuable running time.
But it was Vettel who would clock the fastest time of 1minute 29.16seconds in his Ferrari to draw first blood in his duel with Hamilton.
Hamilton had been faster for the earlier parts of the session but the Mercedes driver had to settle for second spot.
The Briton spoke on Thursday of preparing for "war" in his battle for the championship he currently leads by 34 points - and it may turn out to be a fight on two fronts as the Red Bull was also quick.
Daniel Ricciardo put his car third, just over 0.1seconds behind Hamilton with the second Ferrari of Kimi Raikkonen fourth.
Hamilton's team-mate Valtteri Bottas has admitted he has been struggling with the car lately and he set the fifth-fastest time of the morning.
Next up was Max Verstappen, winner for Red Bull last time out in Malaysia, who took a trip over the dirt before a red flag stopped the session with just under half of the 90 minutes remaining.
It was the Toro Rosso of Carlos Sainz that caused the delay as the Spaniard ran too high onto a curb before hitting the barrier.
Once Sainz's stricken car had been removed and the session restarted Vettel went out on the faster, supersoft tyre and was soon topping the timesheet.
The rain began to fall inside the final 15 minutes and, with no-one improving on their times, Esteban Ocon was seventh for Force India ahead of the Renault of Nico Hulkenberg.
Romain Grosjean took ninth for Haas while Stoffel Vandoorne rounded out the top 10 for McLaren.