F1 championship leader Max Verstappen started his Styrian GP weekend on the right foot by setting the pace in opening practice at the Red Bull Ring.
At the start of two consecutive weekends for F1 at Red Bull's short but challenging home circuit, Verstappen made the early running on soft tyres with a best lap of 1:05.910.
Lewis Hamilton was third, four tenths adrift, as AlphaTauri's Pierre Gasly made it a Red Bull-owned one-two at the top of the timesheet.
Indeed it proved a strong morning for Red Bull's sister team as Yuki Tsunoda claimed fifth, just behind the second Mercedes of Valtteri Bottas.
"The session wasn't great," said Mercedes boss Toto Wolff to Sky Sports F1. "The main loss [for Mercedes] is straight-line speed. If we were racing this afternoon it wouldn't be pretty."
Sergio Perez finished down in 13th in the other Red Bull, with the Mexican spinning during his soft-tyre run at Turn Four.
Carlos Sainz was another driver to spin, with the Ferrari briefly blocking the pit-exit slip after the Spaniard lost control at the first corner.
Teams were especially keen to maximise their morning running in the hour-long session given weather conditions are uncertain for the afternoon's Practice Two running. All but one driver completed over 30 laps.
"It's even harder to read than normal because teams were bargaining on a wet session later on," said Sky F1's Martin Brundle. "So they would have mixed strategies there with tyres and fuel loads between their cars to try to expedite the work they have to do on a Friday."
Hamilton and Verstappen were among the drivers to lose lap times for track limits infringements for running too wide at the final corner, Turn 10.
Alpine's Fernando Alonso had several of his laps deleted during the course of the hour but the in-form Spaniard still finished a promising sixth quickest, just ahead of team-mate Esteban Ocon.
Lance Stroll was the lead Aston Martin in eighth place - team-mate Sebastian Vettel was down in 14th - ahead of Alfa Romeo's Antonio Giovinazzi and Ferrari's Charles Leclerc.