Valtteri Bottas - the first driver to venture out on the track, fifteen minutes into the session - was second fastest for Williams, just ahead of Force India's Sergio Perez and Toro Rosso's Carlos Sainz, with Haas's Esteban Gutierrez completing the top five.
The session began amid heavy rainfall, but conditions soon began to improve as the rain abated and more cars began to circulate. Kimi Raikkonen had set the initial pace for Ferrari on Pirelli’s full wet tyres with 2m 00.812s, but with around 15 minutes remaining Vettel emerged on intermediates and lapped his SF16-H in 1m 57.351s.
That ultimately survived a rash of late improvements by other drivers, and in the end Bottas’s best intermediates lap of 1m 58.061s was 0.710s shy of the Ferrari.
Red Bull had been the first to switch from full wets to intermediates with 24 minutes to go, but both Daniel Ricciardo and Daniil Kvyat joined the Mercedes and McLaren duos, all of whom elected to save their intermediates for qualifying and thus did not record times. Neither did Romain Grosjean, whose Haas lost its telemetry, nor Marcus Ericsson, whose Sauber had a technical problem.
There were several off-track moments throughout the session as drivers struggled to keep control of their machines on the greasy surface, though Grosjean was the only spinner. Jolyon Palmer meanwhile suffered a right-rear puncture on his Renault early in the session.
The conditions are unlikely to clear up prior to qualifying, when the 2015-style system will be reinstated, so the grid could be something of a lottery.