Lewis Hamilton started Formula 1's new season with a dominant display in Friday practice for the Austrian Grand Prix, but took his performance "with a pinch of salt".
The six-time F1 champion topped the timesheet at both the end of first and second practice at the Red Bull Ring, finishing 0.356secs and 0.197s clear of team-mate Valtteri Bottas respectively.
As for Mercedes' rivals, in each session, the best of the rest was a further half-a-second off the pace. Just over two hours after the end of FP2, however, the W11 was protested against by Red Bull, notably its DAS (dual-axis steering) system.
Speaking prior to the protest, Hamilton said: "It's great to be back. It's been a long time coming.
"The new car obviously feels different than the 2018 car we got to test at Silverstone a few weeks ago, but I think we have also been able to continue to improve the car compared to last year, so that's a big positive.
"It was looking good out there today, but you can never take too much from practice. You never know what power and fuel other teams are running.
"So we will take today's result with a pinch of salt, try and improve the car tonight and come back for the fight tomorrow."
Bottas, meanwhile, claimed he "enjoyed every single lap, every single run", but like Hamilton exercised a degree of caution.
"We've been making good progress throughout the day, step by step, as it is to be expected after such a long break," said Bottas.
"It was a decent day overall, although we had a small problem with my car towards the end.
"The main challenge will be to get the balance right for both high-speed and low-speed corners and fine-tune the car for that single lap on Saturday, while keeping our race pace in mind as well.
"It's only Friday, the lap times will come down tomorrow with the track improving, with additional performance items from all the teams and with the drivers pushing hard, so it will be interesting to find out where we stand."
Before you go...
Red Bull launch official protest against Mercedes' DAS system
Verstappen broke Red Bull front wing during fastest practice lap
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