Lewis Hamilton's assault on a seventh world championship has been thrown into deep uncertainty after Red Bull launched an official protest against the Briton's Mercedes car.
Hamilton, who is this season bidding to equal Michael Schumacher's record collection of titles, lit up the time charts in Spielberg as Formula One roared back into action 215 days after last year's concluding round in Abu Dhabi.
Hamilton was quickest in both sessions, finishing two tenths clear of his Mercedes team-mate Valtteri Bottas. Remarkably, no other driver was within half a second of the six-time world champion.
But his team are now being investigated by Formula One's sporting federation, the FIA, after rivals' Red Bull demanded to know whether Mercedes' controversial Dual-Axis Steering (DAS) system is legal.
The device, which the sport's all-conquering team first unveiled at testing in February, has already been banned for 2021.
It enables Hamilton and Bottas to pull the steering wheel towards them, narrowing the alignment of the front wheels on the Mercedes and increasing straight-line speed. They can also push the wheel away before cornering to improve the machine's set-up.
Mercedes, who liaised with the FIA as they spent more than a year developing the concept, were already braced for a protest.
The outcome which could determine the direction of Hamilton's historic title bid, now sits in the hands of the stewards. All parties will be hopeful a resolution is completed before qualifying on Saturday afternoon.
Hamilton's boss, the Mercedes team principal Toto Wolff, had earlier pleaded with his Red Bull counterpart, Christian Horner, not to overshadow the first global sport event of the Covid-19 era by launching a protest following the chequered flag.
Such a move would have delayed the official classification until hours after the finish.
"It is the first race, and although it is fair enough to seek clarification on the other side we don't want to end up with a big debate on Sunday," said Wolff.
"All teams are pretty much aware that we are in a sensitive situation by going racing. I think Christian is going to take the right decision.
"Controversy on engineering innovation has always been a part of Formula One and this has to be expected. It is part of the risk.
"We think we are on the right side, and that is the reason we have it on our car."
With Ferrari off the pace – Sebastian Vettel finished fourth, sixth tenths down on Hamilton, while team-mate Charles Leclerc was ninth – Red Bull's Max Verstappen is set to be Hamilton's closest challenger during this truncated campaign. Sunday's race is the first of eight scheduled rounds in just 10 weeks.
The Dutchman, who won here last year and in 2018, finished third in the opening running before damaging his front wing in the day's concluding session.
Red Bull feel they have taken great strides with engine partner Honda during the prolonged break to provide the most exciting talent on the grid with a car capable of ending Hamilton's dominance.
"Obviously we do want clarity on DAS because it does have an impact regarding the rest of this year," said Horner.
"It has been outlawed for 2021 so the question for us is whether it complies with the regulations in what is a fundamentally grey area. This is what we will be asking the FIA through the necessary channels."
Despite the protest, Hamilton was in a positive mood. "It was great to be back because it has been a long-time coming," he said. "It is difficult to say if we have an edge as you can never take too much from practice so we will take the result with a pinch of salt and try and improve the car tonight."
The Silverstone-based Racing Point team could provide the surprise of the campaign after basing their new design on last year's Mercedes. Their Mexican driver Sergio Perez finished third in the day's concluding practice session.
Lando Norris, 20, was an encouraging sixth for McLaren.
