Lewis Hamilton was significantly quicker than Mercedes team-mate Nico Rosberg in second practice at the Austrian Grand Prix.
Hamilton was 0.377 seconds clear of Rosberg, a large margin on a lap of only 70 seconds at the Red Bull Ring.
Ferrari's Fernando Alonso was third, a second adrift of the Mercedes but just 0.05secs clear of the Williams of Valtteri Bottas and Felipe Massa.
Red Bull's Sebastian Vettel was sixth ahead of Jenson Button's McLaren.
Red Bull's Daniel Ricciardo was eighth, ahead of Button's team-mate Kevin Magnussen, with Toro Rosso's Jean-Eric Vergne 10th.
"This morning we struggled a little bit," said Vettel. "This afternoon it was a bit better. People struggled to get the harder tyre to work. It should be a different story tomorrow when it's a bit hotter."
Mercedes again appear to be in a league of their own at the front, untouchable whether on single-lap qualifying style pace or on the race-simulation runs later in the session.
Rosberg said he was not concerned by the gap between himself and Hamilton.
"It was there in Montreal also, but when it came to qualifying I was right where he is," he said.
"I need to work hard tonight for sure and find some more lap time.
"It's so close between us. I'm hoping we still have the edge on everyone else - it seems to be the case today - so it's going to be between us for pole and it's very important because race pace is going to be close, and to get into the first corner first is a huge advantage."
Hamilton added: "I'm sure Nico has some time in his pocket."
Alonso looked more competitive than Ferrari had for a while, apparently able to mix it with the Williams cars as best of the rest.
But Ferrari also appeared to have made a step forward with some upgrades at the previous race in Canada only to slip back on Saturday and Sunday when they had to abandon some of the new parts because of overheating problems.
BBC F1 analyst Allan McNish said: "The big question is why is Lewis Hamilton able to drag four tenths out over Nico Rosberg? The gap has never been that big this season.
"But Rosberg will be able to look into that and work out where the time is.
"Ferrari look better - can they maintain that in a way they could not in Canada? And Red Bull will want to be closer to the pace at their home track than they have been so far."
Threatened rain never arrived, despite black clouds covering the circuit towards the end of the session, and running finished in sunshine in the picturesque setting of the Styrian mountains, which is hosting a grand prix for the first time since 2003.
Most of the drivers were finding difficulties with the quick penultimate corner, the Rindt Kurve - many of them running wide at one time or another.
The issue of going beyond track limits there is to be discussed with race director Charlie Whiting at the drivers' briefing later on Friday.