Maverick Vinales defied dust and desert winds to set the fastest practice time for the season-opening Qatar MotoGP, overshadowing nine-time world champion and Yamaha teammate Valentino Rossi, who struggled in ninth place.
Vinales, the 22-year-old Spaniard who switched from Suzuki for the 2017 world championship, was almost one and a half seconds clear of 38-year-old Rossi.
The Honda duo of defending world champion Marc Marquez and Dani Pedrosa were second and third fastest at 0.596sec and 0.894sec respectively off the pace.
"The track was a little bit dirty and windy on the first couple of laps, but then the wind calmed down so we had more power on the bike and that helped a lot," said Vinales, who comes into Sunday's race having also dominated winter testing at Valencia, Sepang, Phillip Island and Qatar.
"The first laps were quite difficult with the wind, there wasn't a lot of grip on the circuit, but suddenly the track improved a lot and when I put in the new tyre I just had to push and go for it."
Rossi, a four-time winner in Qatar, admitted his Yamaha was struggling to match the pace of Vinales, who was only two years old when the great Italian won his first world title on a 125cc machine in 1997.
"The performance was not fantastic, but I'm in the top ten and this is good because we don't know what the conditions will be like tomorrow," said Rossi, who was hoping to find pace on Friday when rain is expected to sweep the track.
"With the softer tyre I thought I would be able to push a bit more and improve by some tenths, but with the race pace we are a bit far behind and we have to find something better."
Marquez, who has won three of the last four world titles and triumphed under the Qatar floodlights in 2012 and 2014, admitted that Vinales was the man to beat in Sunday's race.
"Maverick is really fast but it was to be expected," said the Spaniard.
Practice times on Thursday for Sunday's season-opening Qatar MotoGP at Losail:
1. Maverick Vinales (ESP/Yamaha) 1:54.316, 2. Marc Marquez (ESP/Honda) at 0.596, 3. Dani Pedrosa (ESP/Honda) 0.894, 4. Jonas Folger (GER/Yamaha) 1.271, 5. Jorge Lorenzo (ESP/Ducati) 1.291, 6. Loris Baz (FRA/Ducati Avintia) 1.308, 7. Cal Crutchlow (GBR/Honda) 1.323, 8. Johann Zarco (FRA/Yamaha Tech 3) 1.476, 9. Valentino Rossi (ITA/Yamaha) 1.483, 10. Aleix Espargaro (ESP/Aprilia) 1.556
1. Thomas Luethi (SUI/Kalex) 2:00.422, 2. Takaaki Nakagami (JPN/Kalex) at 0.080, 3. Miguel Oliveira (POR/KTM) 0.133, 4. Franco Morbidelli (ITA/Kalex) 0.180, 5. Alex Marquez (ESP/Kalex) 0.226
1. Philipp Ottl (GER/KTM) 2:06.981, 2. Joan Mir (ESP/Honda) at 0.258, 3. Gabriel Rodrigo (ARG/KTM) 0.399, 4. Juanfran Guevara (ESP/KTM) 0.407, 5. Romano Fenati (ITA/Honda) 0.433