Spaniard Jorge Lorenzo recorded the quickest time in practice on Friday for the German Grand Prix at the Sachsenring, with championship leader Marc Marquez fifth fastest.
Three-time MotoGP world champion Lorenzo clocked a best time of one minute and 20.85 seconds on his Ducati.
Danilo Petrucci, who is reportedly replacing Lorenzo at the factory Ducati team next season when the Spaniard leaves for Honda, was second on a Ducati Pramac, 0.257sec behind.
Andrea Iannone, who recorded the best time in the opening session, was third for Suzuki at 0.319sec while Andrea Dovizioso was fourth on the second factory Ducati.
"We have a good opportunity here to fight for the podium and victory is not impossible," Lorenzo told the MotoGP website.
Reigning world champion Marquez has won the top-class race at the Sachsenring for the last five years and is bidding for his ninth straight German GP win in total.
The Honda rider, who leads the riders' standings by 41 points from Italian great Valentino Rossi, was 0.464sec slower than Lorenzo.
"It was a good first day, even if our opponents are all closer compared to last year," Marquez said. "Tomorrow we'll try and take another little step with the setup, because I'm not yet able to make the bike slide like I want."
Yamaha struggled all day, though, as Maverick Vinales had to settle for the sixth-quickest time, with the 39-year-old Rossi all the way down in 17th place.
"When we try to put power on the ground we spin the tyre a lot and we suffer, because when we lose acceleration we lose drive," lamented the nine-time world champion.
"We tried to do something about it this afternoon, but unfortunately we weren't able to improve. We have to continue and try to be stronger tomorrow."
Marquez's Honda team-mate Dani Pedrosa, who announced on Thursday that he will end his 17-year career at the end of the season, was almost a second-and-a-half down on Lorenzo in 20th on the timesheets.
The surprise of the day was Japanese rider Takaaki Nakagami, who was seventh, while Finn Mika Kallio, a KTM wild-card, was taken to hospital for tests after injuring his right knee in a fall.
In Moto2, Spaniard Xavi Vierge edged compatriot Alex Marquez and German Marcel Schroetter.
In Moto3, German Philipp Oettl, on a KTM, finished faster than the Hondas of Italian Tony Arbolino and Spaniard Jorge Martin, the championship leader.
German MotoGP free practice combined times on Friday:
1. Jorge Lorenzo (ESP/Ducati) 1min 20.885sec, 2. Danilo Petrucci (ITA/Ducati Pramac) at 0.257, 3. Andrea Iannone (ITA/Suzuki) 0.319, 4. Andrea Dovizioso (ITA/Ducati) 0.424, 5. Marc Marquez (ESP/Honda) 0.464, 6. Maverick Vinales (ESP/Yamaha) 0.499, 7. Takaaki Nakagami (JPN/LCR Honda) 0.562, 8. Jack Miller (AUS/Ducati Pramac) 0.612, 9. Cal Crutchlow (GBR/LCR Honda) 0.655, 10. Alvaro Bautista (ESP/Ducati Angel Nieto) 0.683
Jorge Lorenzo was fastest on Friday in practice for the German Grand Prix at the Sachsenring.