The Honda rider fell at Turn 2 at the end of the afternoon session - his 26th crash of the season - and ended up fifth-fastest, two places behind title rival Andrea Dovizioso. Marquez walked away from the crash unharmed, but it's a less than optimal start for the Spaniard.
He added: "For some reason this year we are fast, but it's so hard to understand where the limit is".
As most switched to fresh soft slicks for a time attack at the end of the session, Marquez chose to simply have the hard front and soft rear he had been using switched over to his other bike to evaluate different set-ups.
In seven seasons together, Lorenzo and Rossi never scored as few points between them as Rossi and Vinales have mustered this season (423 with a race to go), taking as many as 655 in 2015 and achieving their lowest combined figure, 482, the following season.
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Five overs later, Beth Mooney (27) was caught in nearly identical circumstances to give Sophie Ecclestone her first Test wicket. This time it was Mooney who departed, in an nearly action replay of Bolton's dismissal.
The Gran Premio de la Comunitat Valenciana will be the deciding round between Marc Marquez (282 points) and Andrea Dovizioso (261 points) for the 2017 MotoGP Riders World Championship. Regarding the track, I feel good because I like Valencia.
The Italian is struggling to get the bike settled mid-corner and is losing time to not only Marquez but also team-mate Dani Pedrosa. Of course it's also good to have a points advantage to manage. We tried two different setups, one similar to what we used past year and one more based on what we've been using recently. "We'll keep the same mentality and working method that have brought us to where we are, and we'll give 100 per cent because it will be important to be fast beginning with FP1".
"I am not smooth enough so we have to focus on that".
In Valencia, Marc will take the title if Dovizioso does not win the race, or if Dovizioso does win and Marc finishes 11th or better.