Red Bull's Max Verstappen was fastest in first practice at the British Grand Prix ahead of Mercedes' Lewis Hamilton.
Verstappen was 0.474 seconds clear of the world championship leader but used a softer tyre than Hamilton, whose team start the weekend as strong favourites.
Racing Point's Lance Stroll was third, ahead of Red Bull's Alexander Albon.
Nico Hulkenberg, a last-minute sub for Sergio Perez after the Mexican contracted coronavirus, was a creditable ninth on his return to F1.
The German, who was 0.588 seconds slower than Stroll, had his position confirmed only minutes before the session started because of the wait to confirm he did not have coronavirus.
- British Grand Prix first practice results
- Hulkenberg to stand in for Perez after positive Covid-19 test
Perez's positive test emerged on Thursday afternoon and Racing Point chose Hulkenberg over Mexican Esteban Gutierrez.
Hulkenberg, who was out of F1 after being dropped by Renault last season, was preferred because of his long experience, both in F1 and with the team, having driven for them when they were known as Force India in 2012 and 2014-16.
The session took place under cloudless skies and in soaring temperatures of more than 30C.
In any other year, the circuit would have been teeming with tens of thousands of fans soaking up the sun and enjoying their experience of F1. But the usual festival atmosphere of the British Grand Prix is absent as a result of the lack of fans, who have had to be kept away as a result of the pandemic.
All the British drivers have spoken of how "weird" the event feels without fans, but none will find that more than Hamilton, who has made his home race his own with a record six victories.
Hamilton took the championship lead for the first time this year with victory in the last race in Hungary, the third of the season, and is looking to extend it over two races at Silverstone on successive weekends.
He started the weekend looking strong but quickly rejected the 'soft' tyre that Verstappen used to set his fastest time, with the Briton saying: "Let's get off this tyre, it's terrible." His fastest time was set on the medium.
Other than that, the morning was smooth, although Mercedes have fitted a new MGU-K to his car - a part of the hybrid system - after seeing some anomalies on the data in Hungary.
All other Mercedes engines will have the same part fitted at the next race as a reliability upgrade and the team say it should not lead to grid penalties for Hamilton later in the season.
Team-mate Valtteri Bottas, meanwhile, was down in sixth place, a second off Verstappen and 0.6 seconds behind Hamilton, but used the 'hard' tyre for his best lap.
Albon has a new engineer for this weekend as Red Bull seek to help him get to grips with a difficult car, and it is a return for Simon Rennie, who previously worked with Daniel Ricciardo from 2014-18.
Ferrari's Charles Leclerc was fifth fastest, while the Renaults of Esteban Ocon and Daniel Ricciardo were seventh and eighth. The Frenchman trialled upgraded bargeboard and floor, while the Australian ran the standard parts to compare. Their times were just 0.017 seconds apart.
Leclerc's team-mate Sebastian Vettel missed most of the session after an intercooler problem was discovered on his car. He had to stop so Ferrari could repair it in time for this afternoon's second session.
McLaren's Lando Norris, fourth in the championship heading into the weekend, was only 13th, a place behind team-mate Carlos Sainz.
Norris is running a new helmet colour scheme, the result of a competition he ran for fans, from which he chose a design by a six-year-old girl called Eva.
The session was stopped for 12 minutes after a spin at Becketts by Alfa Romeo's Antonio Giovinazzi, who returned to the pits with all four tyres damaged and rubber flailing and damaging his car.
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