Force India driver Nico Hülkenberg topped a disrupted opening practice session for the Russian Grand Prix at the Sochi Autodrom.
The start of the session was delayed by half an hour, following a suspected diesel spillage between Turns 6 and 10 earlier in the morning.
Track workers cleared the spillage but the circuit in that area was left soaked, leaving drivers to use Intermediate tyres, as Ferrari’s Sebastian Vettel described the situation as a ‘mess’, with the remainder of the circuit bone dry.
Fernando Alonso and Marcus Ericsson conducted the majority of the running for the next half an hour on Prime tyres, with the pair skating through the affected wet area, which showed little signs of drying.
With 15 minutes remaining more drivers began to head out onto the circuit and the times gradually lowered, despite the threat of light rain lurking in the region.
Top spot exchanged hands several times across the final few minutes and Hülkenberg was one of the last to cross the line, posting a 1:44.355 to end quickest.
Mercedes' Nico Rosberg was second, ahead of Vettel, Sergio Pérez, Daniel Ricciardo and Carlos Sainz.
Lewis Hamilton had posted a rapid second sector time but spun at the penultimate corner and settled for seventh.
Valtteri Bottas slid through the final corner en-route to eighth, while Max Verstappen and Kimi Räikkönen completed the top 10, the latter spinning at the wet Turn 8.
Button and Alonso ultimately wound up in 11th and 14th places respectively, split by Brazilian pair Felipe Massa and Felipe Nasr, the former suffering a spin exiting the damp Turn 8.
Pastor Maldonado was 15th, ahead of Daniil Kvyat and Lotus reserve driver Jolyon Palmer.
Roberto Merhi and Will Stevens were 18th and 20th, while Ericsson suffered a problem while trying to leave the pit lane during the closing stages of running and was left down in 19th.