PHILLIP ISLAND: Reigning world champion Valentino Rossi held the edge over Casey Stoner with the best time in opening free practice at the Australian Grand Prix here on Friday.

Rossi, who leads his Fiat Yamaha teammate Jorge Lorenzo by 18 points heading into the third-last MotoGP of the season, set the fastest time in the session with one minute 31.032 seconds.

The Italian six-time premier class world champion looked comfortable in completing 31 laps of the island circuit in dry conditions.

"Today we made a great start," Rossi said. "I am really happy to start in front at Phillip Island, which is where I love to ride.

"We were able to get a lot done in the practice session and we can definitely improve more, even though we already have a good pace."

His time was 0.135sec better than Ducati racer Stoner, who is bidding for a hat-trick of wins in his home GP this weekend.

Stoner, who returned to the championship at the last Portugal MotoGP after missing three races through illness, clocked his best time of 1:31.167 on the last of his 22 laps.

Stoner is trailing Repsol Honda's Dani Pedrosa of Spain by three points in the chase for third place in the championship.

"I'm not that happy with today's session," Stoner said. "The track conditions weren't good at all and I struggled for traction, which is usually a strong point of our bike.

"The front end was quite consistent throughout so it's just a case of working on the rear tomorrow and hoping the track conditions improve so that we can find where the limits are."

Pedrosa, looking to make amends for his crash in last year's race, posted the third best time of the first session and was 0.496sec down on Rossi's pace.

"We were lucky with the weather today and I'm happy with how the first practice has gone. I'm sure the times will drop more tomorrow," Pedrosa said.

Lorenzo, who low-sided near the end of the session and came off his Yamaha, could only manage the sixth best time, 1.045 behind his teammate Rossi.

"I think I ate something last night which didn't agree with me and I felt very weak today," Lorenzo said.

"We had some spin and not enough grip or confidence and twice I nearly crashed before I actually did.

"Luckily, I didn't hurt myself and I will try to get a good night's sleep and hopefully I'll be much better tomorrow."

San Marino's Alex de Angelis (Honda) and American Colin Edwards (Yamaha) were fourth and fifth, both lapping within a second of Rossi.

Italian Niccolo Canepa, riding a Ducati, hit the track and was taken to the medical centre for a check-up on his right elbow, but only suffered bruising and is expected to ride in Saturday's qualifying.