Maverick Vinales was quickest on the opening day of MotoGP post-season testing at Valencia with a 2016-spec chassis on his Yamaha as his teammate Valentino Rossi suffered a big crash early on.
While 2017 champion Marc Marquez was leading for the majority of the day, Johann Zarco and then Vinales demoted the Honda rider as the final hour approached.
Vinales set his benchmark time of 1m30.189s with a 2016 chassis and, while the team did not confirm the exact specification of the bike, it is believed that the Spaniard was using a development 2018 engine.
He also trialled a radical new aero fairing during the day.
His teammate Rossi also had a competitive day in fourth, despite suffering a violent crash early in the day.
The Italian went off at Turn 10 and, while his bike suffered massive damage, he escaped the incident unhurt.
Satellite rider Zarco finished the day as runner-up, two tenths off Vinales, having set his best time on the 2017-spec Yamaha bike.
Marquez led Honda's efforts in third, the brand bringing 2018 prototypes, chassis and engine, for him, Dani Pedrosa and Cal Crutchlow.
However, Marquez's top time of 1m30.501s was set with the Honda he used this year.
Jack Miller completed a positive day on his debut with Pramac Ducati, as he was the Italian manufacturer's fastest representative in fifth.
Factory riders Andrea Dovizioso and Jorge Lorenzo were seventh and eighth, also behind Aprilia's Aleix Espargaro.
With Ducati set to wait until next year to debut the Desmosedici GP18, both factory riders along with Danilo Petrucci were testing an evolution of the 2017 bike.
KTM duo Pol Espargaro and Bradley Smith were ninth and 12th respectively, sandwiching the Honda duo of Crutchlow and Pedrosa.
Tito Rabat completed his first day with Avintia Ducati in 13th, as Aprilia debutant Scott Redding was 15th.
LCR Honda's Takaaki Nakagami was the top rookie rider in 17th, 2.5s off the pace.
Reigning Moto2 champion Franco Morbidelli was just four hundredths of a second slower in 18th, as the order was completed by Takumi Takahashi, who replaced the injured Tom Luthi at Marc VDS Honda, and Avintia Ducati's Xavier Simeon.
Suzuki was forced to skip the day as both Andrea Iannone and Alex Rins, along with other team members, were diagnosed with minor viral infection.
Alvaro Bautista also failed to set a laptime due to a violent highside crash at Turn 1, caused by a suspected gearbox failure in his Aspar Ducati bike.
The Spaniard went to the hospital for checks, but he was cleared of any fractures.
His teammate Karel Abraham and Simeon also fell during the day.
Day 1 results
|2||Johann Zarco||Tech 3 Yamaha||1:30.389|
|5||Jack Miller||Pramac Ducati||1:30.635|
|10||Cal Crutchlow||LCR Honda||1:31.259|
|13||Tito Rabat||Avintia Ducati||1:31.673|
|14||Danilo Petrucci||Pramac Ducati||1:31.721|
|16||Karel Abraham||Aspar Ducati||1:32.445|
|17||Takaaki Nakagami||LCR Honda||1:32.723|
|18||Franco Morbidelli||Marc VDS Honda||1:32.762|
|19||Takumi Takahashi||Marc VDS Honda||1:33.569|
|20||Xavier Simeon||Avintia Ducati||1:34.242|
|NC||Alvaro Bautista||Aspar Ducati|