Reigning MotoGP world champion Casey Stoner edged out title rival Valentino Rossi to set the fastest lap on the opening day of the Czech Republic Grand Prix, despite suffering the effects of an illness, which has left him weak and unable to ride at the maximum of his ability.

Nevertheless, the Australian still managed to overturn Rossi's first free practice advantage during the afternoon session, which he finished just 0.179secs in front of the Fiat Yamaha rider, despite running off track in the closing minutes.

"Unfortunately I've not been feeling well for a few days and I felt very weak today - I even felt sapped of energy just putting my gloves on," explained the Ducati Marlboro star, beaten by Rossi in a thrilling duel last time out at Laguna Seca. "I can deal with a bit of tiredness but this afternoon I could only ride a handful of laps before I started to feel cramps in my stomach.

"That doesn't help my crew because I've not been able to put many consecutive laps together and this morning wasn't too good for us, we struggled to find the right set-up for this new surface. To look at you'd think it would be smooth on the tyres but it's actually quite aggressive, particularly on the front.

"This afternoon we went with a harder compound front tyre - similar to what we used at Laguna and Sachsenring, which is about the hardest we've got - and we had to work on the geometry to get the most effective load on the front tyre.

"The guys improved the bike every time I came in so it was frustrating not to be able to put it all together with a long run. We still have a lot of work to do so hopefully I'll feel better tomorrow and the weather holds out for us," added Stoner, referring to the heavy rain that fell shortly after the end of the second MotoGP free practice session.

Team-mate Marco Melandri scored a better than usual tenth in first practice, but dropped down the timesheets to 15th this afternoon. The Italian's target tomorrow is to improve his feeling with the bike, particularly with the rear end.

"We started out well this morning and did some decent lap times but in the afternoon we didn't manage to make progress with the set-up and as the other riders improved we lost more and more ground," confirmed Marco, who had been tipped to split from Ducati before this weekend's event. "The bike is moving around a lot, especially on the rear, so that's an area we have to work on tomorrow - weather permitting. The new surface has improved the track overall although there are still a few bumps here and there."