Australian Jack Miller delivered the best time in practice on Friday ahead of the Valencia MotoGP as Joan Mir crashed to fall outside the top 10, with the Spaniard's first world title in sight this weekend.
Mir suffered a late blip at the Ricardo Tormo circuit when he came off at Turn 4 with 11 minutes to go, an error that saw him drop to 11th in the standings.
But after clinching his maiden premier category victory on the same track in the European Grand Prix last weekend, Mir will become world champion on Sunday if he finishes on the podium.
The Suzuki rider's main challengers are Alex Rins and Fabio Quartararo, but of the top three only Rins holds a provisional Q2 spot after he came eighth in the afternoon practice session, ahead of his Spanish compatriots Aleix Espargaro and Maverick Vinales.
France's Quartararo came 16th, despite being only 0.704sec behind in an incredibly tight leaderboard.
Miller's time of 1min 30.622sec was enough for the Pramac Ducati rider to claim the fastest lap of the day, which for a while belonged to Japan's Takaaki Nakagami, who had set the pace with 1min 30.713sec on his LCR Honda.
Italian Francesco Bagnaia completed the top three, just ahead of KTM's Pol Espargaro.
Mir had been eighth fastest in the morning session but a low-key day for the 23-year-old will not be too much of a concern, given he takes a commanding 37-point lead into Sunday's race.
He needs only 14 points to be crowned champion and could secure the title if he finishes fourth, as long as neither Quartarao or Rins win the race.
It would mean Mir celebrating with a week to spare, the season finale taking place at Portimao in Portugal on November 22.
Combined fastest times from Friday's opening practice sessions at the Valencia MotoGP in Spain
1. Jack Miller (AUS/Ducati-Pramac) 1:30.622, 2. Takaaki Nakagami (JPN/Honda-LCR) at 0.091sec, 3. Francesco Bagnaia (ITA/Ducati) 0.120, 4. Pol Espargaro (ESP/KTM) 0.199, 5. Johann Zarci (FRA/Ducati) 0.277, 6. Andrea Dovizioso (ITA/Ducati) 0.304, 7. Cal Crutchlow (GBR/Honda) 0.308, 8. Alex Rins (ESP/Suzuki) 0.325, 9. Aleix Espargaro (ESP/Aprilia) 0.367, 10. Maverick Vinales (ESP/Yamaha) 0.440