World championship leader Fabio Quartararo was quickest in practice at Silverstone on Friday, ahead of MotoGP's resumption after a five-week break at the British Grand Prix.
The Yamaha rider, who won this race last year on the way to his first world title, topped the practice charts, 0.154secs ahead of Suzuki's Joan Mir.
Aleix Espargaro (Aprilia), who is Quartararo's closest challenger 21 points adrift in the title race, was fifth fastest, 0.207secs behind the flying Frenchman.
Quartararo had the minor embarrassment of breaking down during the first session when Jack Miller gave him a tow back to the pits and also spent much of his time on track practicing the 'long lap' that he will need to do early in Sunday's race.
It is a penalty he collected in the last race in the Netherlands when he was judged culpable for a crash that sent Espargaro into the gravel.
"It will cost me time but the main difficulty will be to get back out (on the race track) in the same trajectory as the other pilots, without being able to do very much", the 23-year-old said after a "hard" but "positive" practice around then 'long lap'.
Two of Quartararo's nearest rivals also suffered in the first session with fellow Frenchman Johann Zarco (Ducati-Pramac), who is third in the championship, and Francesco Bagnaia (Ducati), who is fourth, both crashing.
Zarco said he was "happy" with Friday's practice in spite of the fall "which puts my brain back in place a bit".
"I was able to attack again immediately," he said. "The speed is there, I'm working to find consistency and have a bike that suits me better".
Top practice times:
1. Fabio Quartararo (FRA/Yamaha) 1.58:946, 2. Joan Mir (ESP/Suzuki) at 0.154, 3. Maverick Vinales (ESP/Aprilia) 0.177, 4. Johann Zarco (FRA/Ducati-Pramac) 0.188, 5. Aleix Espargaro (ESP/Aprilia) 0.207, 6. Miguel Oliveira (POR/KTM) 0.217, 7. Alex Rins (ESP/Suzuki) 0.300, 8. Enea Bastianini (ITA/Ducati-Gresini) 0.412, 9. Jack Miller (AUS/Ducati) 0.418, 10. Marco Bezzecchi (ITA/Ducati-VR46) 0.432