Misano Adriatico - Maverick Vinales was the fastest of the Yamahas as they dominated Friday's two practice sessions ahead of this weekend's San Marino MotoGP.
The Yamahas took four of the top five spots at Misano, only separated by the Honda of championship leader Marc Marquez who was third quickest.
Vinales, who won the Dutch GP at the end of June, set the pace with a best lap of 1min 32.775secs which was just 0.057secs quicker than his French teammate Fabio Quartararo, who had topped the first session.
Behind Marquez, who has a 78-point lead over Ducati's Andrea Dovizioso in the title race, were the Yamahas of the evergreen Valentino Rossi and Franco Morbidelli.
"Obviously if one of the Yamaha riders goes on to win this race it would be good," said the 20-year-old Quartararo.
"It's always good to have someone pushing your limits and we always look to see who is the top Yamaha rider".
Seven-time world champion Rossi, who has won his home San Marino GP three times, said Quartararo was pressing for a first race victory. The rookie already has three pole positions and three podiums to his credit this season.
"To win a first race, you have to be 100% in every sense and making a good start is essential," said the 40-year-old, now in his 20th season in MotoGP.
"We are not completely ready but we are almost there."
A third free practice session will be held on Saturday morning before qualifying in the afternoon.
1. Maverick Vinales (ESP/Yamaha) 1min 32.775sec, 2. Fabio Quartararo (FRA/Yamaha-SRT) 0.057, 3. Marc Marquez (ESP/Honda) 0.339, 4. Valentino Rossi (ITA/Yamaha) 0.695, 5. Franco Morbidelli (ITA/Yamaha-SRT) 0.749, 6. Pol Espargaro (ESP/KTM) 0.849, 7. Danilo Petrucci (ITA/Ducati) 0.953, 8. Andrea Dovizioso (ITA/Ducati) 1.051, 9. Alex Rins (ESP/Suzuki) 1.099, 10. Cal Crutchlow (GBR/Honda-LCR) 1.132