Max Verstappen ensured Red Bull finished ahead of Mercedes on the opening day of the second leg of F1's Austrian double header, as Daniel Ricciardo crashed out for Renault.
With Valtteri Bottas - last Sunday's race winner - finishing second fastest and team-mate Lewis Hamilton down in sixth, Verstappen topped the session for circuit owners Red Bull - who are bidding to rebound from a disappointing Austrian GP when both their cars retired.
Verstappen's time of 1:03.660 was 0.043s quicker than Bottas' best, with morning pacesetter Sergio Perez third for Racing Point.
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Lance Stroll was fourth in the other Racing Point, with Carlos Sainz fifth for McLaren.
Hamilton was only sixth, with Mercedes confirming during the session that the six-time champion "isn't happy with the car" and that they would be checking the W11 into the evening.
Sky F1's Jenson Button said: "It's just a real mixed-up grid, I think the heat has made a difference."
But the session was one to completely forget for Ricciardo, who crashed his Renault heavily at the penultimate corner.
Ricciardo lost the back end of the RS20 as he turned into the fast right-handed sweep and slewed across the run-off into a collision with the tyre barriers.
The Australian was uninjured, although was seen limping away from the car and then once back in the paddock after returning from a check-up at the medical centre.
Sebastian Vettel, meanwhile, endured another tough session on track and finished only 16th in the partly-upgraded Ferrari, with two of his track times deleted for exceeding track limits. The German finished between the two Williams cars, who have made big improvements from 2019.
Five of the six Ferrari-powered cars were among the bottom eight, with Charles Leclerc the exception in ninth.
Hamilton left with work to do
Concerns among the teams that the possibility of heavy rain could disrupt Saturday's schedule - and even theoretically eventually cancel qualifying altogether if poor weather continued into Sunday morning - meant there was an extra emphasis to normal on low-fuel P2 runs, in case the session ends up forming the grid.
But Hamilton never really never gained any kind of momentum on the timesheet, with his quickest lap ending up some 0.7s off Verstappen's pace.
"It felt relatively normal but quite far off," said Hamilton. "There's a lot of work going on in the background to try and figure out why. But I was feeling good in P1 and then start of P2 but then it started to drop off.
"Others out there are obviously quick and Valtteri's obviously got good pace, so hopefully tomorrow we will be in a bit better position."
He added: "If we have to start [sixth] that would definitely suck if we don't get to qualify, because P2 wasn't great, starting further back than I was even last week.
"It would definitely make it challenging. I'll try to do the dry dance, if there is a dry dance!"
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