Marc Marquez began what could be a title-winning MotoGP weekend at Motegi in an uncharacteristic sixth place, 0.799s from the top.

The Repsol Honda star had an unsettling start to the day when he ran off track after being unable to brake for Turn 5, forcing him to leave his RC213V in the gravel.

"The problem was I had big shake coming onto the straight [which pushed the brake pads away from the disc]. I braked earlier than usual because I expected there could be a little problem, but there was no brake," Marquez explained. "Then I pumped the lever one, two, three times to try and find the brakes, but it was too late to make the corner. Better to happen in practice than the race."

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Marquez soon recovered to finish a close second to Yamaha's Jorge Lorenzo in the opening session, but couldn't keep pace with the afternoon improvements of his rivals.

"Today we struggled a bit compared to other circuits," he admitted. "At the moment I don't feel very comfortable but thankfully it's still only Friday and we have many practice sessions ahead and things to try out. We are not so far from the top so let's see if we can improve over the course of the weekend."

Indeed, with Ducati's Andrea Dovizioso using an extra-soft rear tyre to pull 0.440s clear of the field, Marquez was still within 0.350s of race pace setter Lorenzo.

Marquez will be confirmed as having successfully defended his MotoGP title if he can maintain his present 75 point advantage by the end of Sunday's race. Team-mate Dani Pedrosa, currently Marquez's closest rival, was fourth on Friday.

Even if Marquez is made to wait, he will have three further chances to clinch the 2014 title.