Spain's defending world champion Jorge Lorenzo topped both practice sessions on Friday as title challenger Marc Marquez struck trouble ahead of this weekend's Australian MotoGP at Phillip Island.
Yamaha's Lorenzo clocked one minute 28.961 seconds for the fastest lap in second practice to hold a gap of 0.294secs over compatriot Marquez on a Honda.
But Marquez, who can claim the world title in his debut premier class season if he beats Lorenzo by sufficient points in Sunday's third-last race of the season, came heavily off his bike during the afternoon run.
The 20-year-old Spanish rookie high-sided his Repsol Honda and landed heavily on the newly-laid asphalt surface before getting to his feet.
Appearing to have escaped injury, Marquez was back out on the track less than 20 minutes later.
"It's a pity about the crash right at the start of the afternoon run but we went back out with the second bike, which had a totally different geometry and we had no time in which to change things," Marquez said.
"So we used the initial setup for the entire session. We shall see if tomorrow we can regain the feeling that we had in the morning session, as I felt very good."
Lorenzo, who clinched his world title in last year's race, went within 0.304secs of Australian Casey Stoner's lap record of 1:28.665 set in the 2008 Phillip Island race.
“I feel that here we are much more competitive than in Malaysia," Lorenzo said.
"There are some problems with the wind in some corners where we cannot keep the front wheel on the ground so we need to improve that for tomorrow.
"The new tarmac is much better, you can push with more confidence and there are less bumps.”
Stoner retired from MotoGP at the end of last season in a career where he won six consecutive Australian MotoGPs around Phillip Island.
Spain's Alvaro Bautista had the third-fastest lap Friday, 0.477secs down on Lorenzo with Marquez's Spanish teammate Dani Pedrosa fourth at 0.517secs.
"Today was very positive, the new asphalt felt good and the tyres worked well for us," Pedrosa said.
"The only setback was that we were unable to make the most of all the time available, due to a problem with the bike at the end of the afternoon session."
Seven-time premier class world champion Valentino Rossi was fifth quickest and trailing Yamaha teammate Lorenzo's best time by 0.576secs.
The Italian great has only been off the podium at Phillip Island on three occasions since he debuted in the World Championship in 1996.
“I’m happy about today, especially this afternoon as we were able to improve the settings of the bike a lot. I’m happy about my pace, I’m constant and also quite fast," Rossi said.
Marquez holds a 43-point lead heading into Sunday's Australian showdown and a win, worth 25 points, could land him the title if he outscores Lorenzo by eight points this weekend.
If that happens Marquez would become the first rookie to clinch the premier class championship since American Kenny Roberts in 1978.
LCR Honda’s Stefan Bradl, who fractured an ankle at Sepang last Saturday, was allowed to take part in opening practice but finished almost four seconds off the pace and was later declared unfit.
The German hopes to return in Japan next weekend.