The rain arrived just as running resumed following a brief red-flag period caused by Fernando Alonso stopping his McLaren on the pit straight with more technical woes. It meant numerous drivers found themselves experiencing a lap of a very slippery Spielberg circuit on dry, supersoft tyres.
Mercifully none came to grief, despite some minor off-track excursions, but the change in conditions signalled the end of any lap time improvements, and from there on in everyone confined themselves to wet or intermediate tyre running.
In the dry Vettel had lapped his SF15-T in 1m 09.994s on the soft tyres, knocking Hamilton off the top spot which the world champion had comfortably reclaimed every time Mercedes team mate Nico Rosberg had registered an improvement.
But there were more hints today that Mercedes are expecting trouble from the red cars for the rest of the weekend. These were given more weight when Kimi Raikkonen pushed Rosberg down to fourth, with 1m 10.177s to the German’s 1m 10.332s.
Both Mercedes and both Ferraris were out on supersofts just as the rain came - leading to their respective engineers beseeching them all to take it easy getting back to the pits to avoid damage that might not be rectified in time for qualifying. As it was, Raikkonen slid off the road, but avoided contact with anything.
Sergio Perez was one of few drivers to get a run on supersofts before the rain came and leapt to fourth with a lap of 1m 10.221s, while behind him Williams’ faith in their new aero configuration was fully justified as Felipe Massa and Valtteri Bottas took sixth and seventh on the soft tyres.
Max Verstappen starred yet again for Toro Rosso in eighth, though the young Dutchman and team mate Carlos Sainz - who finished 13th - both suffered hairy spins while running wet tyres towards the end of the session.
The Lotuses of Pastor Maldonado and Romain Grosjean ended up ninth and tenth, just ahead of Force India’s Nico Hulkenberg and Sauber’s Marcus Ericsson. Daniil Kvyat, who faces a 10-place grid drop for an engine change, was 14th for Red Bull having equalled stable mate Sainz’s time.
Alonso’s problem ensured it was another fraught session for McLaren. The Spaniard had completed just 13 laps before coming to a halt, and ended up in 15th. He was already facing a 20-place grid penalty for changing multiple power unit elements, and shortly after the session came confirmation that team mate Jenson Button - who finished down in 18th - will take a 25-place penalty for similar changes.
Red Bull’s Daniel Ricciardo, Sauber’s Felipe Nasr and Marussia’s Roberto Merhi managed the fewest laps in FP3, finishing in 16th, 17th and 20th respectively. Nasr had reported smoke from his car early in the session, while Ricciardo is another driver with an engine-related grid penalty hanging over him ahead of qualifying.
With the prospect of more rain this afternoon, the stage is set for a highly unpredictable qualifying session.