The first of two races at Misano will take place on a newly resurfaced track, with Vinales’ best time of 1m32.198s already a little over half a second off the all-time best lap of 2018.
The San Marino GP is also the first to welcome fans in 2020, with a modest, socially distanced crowd enjoying the MotoGP action on Friday morning.
KTM’s Pol Espargaro set the early pace with a 1:34.115 after being one of a few current racers to test on the new Misano surface in June.
His time was improved five minutes later by Petronas’ Fabio Quartararo, with the Yamaha rider – at the scene of his first duel for victory with Marc Marquez last year – topping the lead with a 1m34.039s.
This was short-lived, however, as Espargaro returned to the top of the standings with a 1m33.607s before factory Yamaha’s Vinales improved to 1m33.479s.
With just under 25 minutes to go, Quartararo took the lead again with a 1:33.435, which served as a benchmark until the closing stages of FP1.
Midway through the session, 2018 Misano race winner Dovizioso proved tricky as several attempts to get onto the track were aborted by a problem with his works Ducati.
Unable to fix the problem, Ducati sent Dovizioso out on his second bike in the final stages, jumping from outside the top 20 to ninth place.
Quartararo put pressure on his own best lap with six minutes to go to set a 1’33.215, which he then improved by 0.126 to 1’33.089.
With two minutes to go, Vinales started lighting up the timing screens again after unusually fitting a fresh, hard rear tire to take the lead with a 1’32.760.
On his last attempt, he blew the field by 0.550s with a 1m32.198s to finish FP1 at Misano – where he took pole last year – ahead of Quartararo.
Unlike its rival manufacturers, Yamaha never tested with Jorge Lorenzo at Misano in June – something Quartararo questioned when asked about it on Thursday.
Aprilia’s Aleix Espargaro was chasing Vinales late and the result jumped to third place with a 1m32.949s ahead of top Ducati rider Johann Zarco on the year-old Avintia GP19 and Bradley Smith’s sister Aprilia.
Joan Mir was fastest Suzuki in sixth ahead of Pramac’s first works Ducati’s Jack Miller, injured LCR Honda rider Cal Crutchlow – who suffered a technical issue in FP1 – Pol Espargaro and Takaaki Nakagami (LCR).
Valentino Rossi was pushed out of the top 10 late for the first session of his home race, followed by Franco Morbidelli (Petronas), KTM’s Brad Binder and Dovizioso.
Alex Rins was a cautious 16th on his Suzuki, while Styrian GP winner Miguel Oliveira was an enigmatic 2.4s off pace in 22nd and last in the first session.