Lewis Hamilton started his 2020 Formula 1 campaign with a powerful statement of intent as he topped the first day of pre-season testing in Spain.
Hamilton and team-mate Valtteri Bottas shared the driving for Mercedes and ended the day first and second fastest.
The world champion was 0.337 seconds quicker than Bottas, who headed Racing Point's Sergio Perez by 0.062secs.
Hamilton's time was set on the 'hard' compound of tyre, whereas Bottas and Perez were on the faster 'medium'.
Bottas described the day as "a nice starting point" and said: "The car feels good."
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Red Bull's Max Verstappen, who had two harmless spins at Turn 13, was fourth fastest at the Circuit de Catalunya-Barcelona, ahead of Russian Daniil Kvyat in the Alpha Tauri - formerly known as Toro Rosso, the Red Bull junior outfit - and Carlos Sainz's McLaren sixth.
The Dutchman said: "I touched once the gravel, that is why I spun. And once I lost it in the same corner. These things can happen trying to see the limits of the car, what you can do. Those things are part of it. Luckily no damage, which at the end of the day is the most important thing.
"It has been a good day; the car has been working really well, and the engine - that's all we want to see. For us it is the most important [thing], I'm very happy about that.
"It is your first time back in the car so of course your neck is always going to be stiff."
Ferrari had a low-key day that started with an enforced driver change.
Four-time champion Sebastian Vettel had been due to drive, but he had to withdraw because he was feeling unwell, and the German went back to the hotel to recover after taking part in an official F1 start-of-term photo with the other drivers.
Team-mate Charles Leclerc took over instead and ended the day only 11th fastest.
Whether deliberately or otherwise, Leclerc's initial notes after his first run in the car were captured on camera, and they said that he had experienced some understeer - lack of front grip - in the long-duration, low-speed corners on the Circuit de Barcelona-Catalunya.
There was an encouraging start to the year for Williams, who are keen to bury memories of last season when they had the worst year in their history, with a car nearly 1.5 seconds slower than the next slowest on the grid.
The lap times were very fast, and there was some amazing reliability - there was not a single on-track failure leading to a red flag during the day, a remarkable feat for the first day of testing.
The final new cars appear
The start of the day was marked by the emergence of the final three cars not to have had an official launch in the run-up to the start of testing - the Alfa Romeo, Haas and Racing Point.
The Racing Point turned the most heads for its similarity in many design aspects to last year's title-winning Mercedes.
Racing Point, who will be rebranded Aston Martin in 2021 following owner Lawrence Stroll's takeover of the sportscar company, have a technical partnership with Mercedes that includes buying the engine, gearbox and suspension from the champions and using their windtunnel.
And although the team are required by regulation to design their own aerodynamic surfaces, they have produced a car that looks in many areas a virtual facsimile of the Mercedes from 2019.
A positive start for Williams
Williams made an encouraging start to their season after the disappointments of 2019, when they were by far the slowest team.
This time last year, Williams did not even have a car ready for the first two and a half days of testing, a failure that ultimately led to the departure of their technical chief Paddy Lowe.
This time, their promising British driver George Russell was first out on track, an achievement Williams described as "cathartic", and he set the eighth fastest time.
Russell said: "It's feeling good. It's definitely an improvement on last year. It's difficult to get a read so far but from within it feels nice to drive. Obviously lap times are the important thing and we'll only know by the end of next week how that is.
"Last year was far from ideal and the team have done a really great job to achieve that and the build quality of the car is so much better standard compared to last year. Things fit properly and the car looks better from a design perspective, so I think overall it's been a very positive morning.
"It was definitely a character-building year last year and I'm confident we can go racing this year and have a bit more fun than last year, and that's what we are all hoping for."
Fastest times, first pre-season test, day one:
1 Lewis Hamilton (GB) Mercedes 1:16.976 H
2 Valtteri Bottas (Fin) Mercedes 1:17.313 M
3 Sergio Perez (Mex) Racing Point 1:17.375 M
4 Max Verstappen (Ned) Red Bull 1:17.516 M
5 Daniil Kvyat (Rus) Alpha Tauri 1:17.698 M
6 Carlos Sainz (Spa) McLaren 1:17.842 H
7 Daniel Ricciardo (Aus) Renault 1:17.873 H
8 Esteban Ocon (Fra) Renault 1:18.004 M
9 George Russell (GB) Williams 1:18.168 M
10 Lance Stroll (Can) Racing Point 1:18.282 H
11 Charles Leclerc (Mon) Ferrari 1:18.289 M
12 Nicholas Latifi (Can) Williams 1:18.382 S
13 Robert Kubica (Pol) Alfa Romeo 1:18.386 M
14 Kevin Magnussen (Den) Haas 1:18.466 M
15 Antonio Giovinazzi (Ita) Alfa Romeo 1:20.096 M
Key: S = soft tyre; M = medium tyre; H = hard tyre