Lewis Hamilton topped a Mercedes one-two in first practice for the Austrian GP in his newly-updated W09 car.
Mercedes have introduced a vast aerodynamic upgrade package for this weekend's race at the Red Bull Ring, featuring changes to their cars' sidepods, bargeboard and rear-wings.
The initial results were encouraging as Hamilton consistently set fastest laps through the session, before ultimately pipping team-mate Valtteri Bottas by 0.127 seconds with a lap of 1:04.839.
"It's pretty tight at the front, there's not much difference between the cars, but it was a good start for us," Mercedes boss Toto Wolff told Sky F1.
Mercedes unleash big car upgrade
Hamilton was fastest early on after running the supersoft tyres but set his quickest time in the final thirty minutes after switching to ultrasofts as the 'new' Mercedes made an instant positive impression.
"It's like a B-spec car almost," commented Sky F1's Martin Brundle. "I think it's very ominous for the opposition. They won't be putting any parts on their car which haven't been validated in the wind tunnel."
As so often this season, the top six positions were exclusively occupied by the 'big three' teams of Mercedes, Red Bull and Ferrari.
At the team's home race in the Austrian mountains, Red Bull pair Max Verstappen, who spun at turn four in the early stages, and Daniel Ricciardo were third and fifth fastest respectively.
Ferrari's Sebastian Vettel, who trails Hamilton by 14 points in the world championship, was fourth fastest ahead of team-mate Kimi Raikkonen. But the Scuderia have regularly run their car at reduced power during Friday practice this season, making their form notoriously difficult to read.
Charles Leclerc, in contention to replace Raikkonen at Ferrari next year, impressed once again as he guided his Sauber to ninth.
Robert Kubica, making his second Friday outing of the year, was slowest of all, but the Pole's work was entirely devoted to car development for the beleaguered Williams team.
McLaren also struggled to impress on the timesheets although Fernando Alonso, 17th and 1.7 seconds adrift of Hamilton's benchmark, set his quickest time on soft tyres, the slowest available.
Stoffel Vandoorne was 18th but, along with the Renaults of Nico Hulkenberg and Carlos Sainz, his car has been boosted by the introduction of a lighter-weight MGU-K unit from the French engine maker.