Doha - World champion Jorge Lorenzo and Yamaha team-mate Valentino Rossi laid down early markers on Thursday when they set the fastest times in first practice for the season-opening Qatar Grand Prix.
Under the Losail floodlights, Lorenzo clocked 1min 55.440sec with nine-time world champion Rossi 0.267sec off the pace.
The Ducatis of Andrea Iannone and Hector Barbera were third and fourth fastest at 0.296sec and 0.370sec behind Lorenzo.
However, the Honda machines of Dani Pedrosa and two-time champion Marc Marquez were only seventh and eighth on the time-sheets, a disappointing start for a team which is traditionally Yamaha's greatest rivals.
"I had a good start. From the first run I was able to have the best lap time and probably also the best pace, but we still have a margin for improvement both in lap time and pace," said Lorenzo, who claimed a third world title last year by just five points from Rossi in a last-race decider.
"We will keep working on the setting and the electronics to improve in some areas for Friday. The track will also be better with more grip level tomorrow and the lap times will be faster."
There are two more sessions planned at the desert venue on Friday before qualifying on Saturday for Sunday's night-time race - the first of 18 rounds.
Italian legend Rossi is starting his 21st season in the world championship and is desperate to make up for the controversy of 2015.
He was within touching distance of a 10th title on his Yamaha only for an ill-judged kick at Honda rival Marquez at the penultimate race in Malaysia.
The 37-year-old was punished by being forced to start the title-decider in Valencia at the back of the grid, a penalty which allowed Lorenzo to take the championship by just five points.
"The first practice was positive. I'm quite satisfied, it was a strong way to start the season, because the second position is good and also the lap times are already not so bad," said Rossi on Thursday.
"The condition of the track changes a lot session by session and together with the team we have to deliver good work so we will be ready when the grip becomes better."
1. Jorge Lorenzo (ESP/Yamaha) 1:55.440, 2. Valentino Rossi (ITA/Yamaha) at 0.267, 3. Andrea Iannone (ITA/Ducati) 0.296, 4. Hector Barbera (ESP/Ducati Avintia) 0.370, 5. Maverick Vinales (ESP/Suzuki) 0.407, 6. Pol Espargaro (ESP/Yamaha Tech3) 0.611, 7. Dani Pedrosa (ESP/Honda) 0.658, 8. Marc Marquez (ESP/Honda) 0.818, 9. Andrea Dovizioso (ITA/Ducati) 0.947, 10. Scott Redding (GBR/Ducati Pramac) 0.972