Jorge Lorenzo put his lack of speed in Friday practice at Phillip Island down to illness as well as a lack of grip.
The title contender was only sixth fastest today, and was a second adrift of his Yamaha team-mate Valentino Rossi. Lorenzo also had a minor crash at the hairpin at the end of the session.
"I just couldn't go fast today," he admitted. "I wasn't feeling too good - I think that I ate something last night which didn't agree with me and I felt very weak, which made it very hard to ride the bike.
"We had some [wheel]spin and not enough grip or confidence and there were two times where I nearly crashed before I actually did.
"Luckily I didn't hurt myself at all and now I will just try to get a good night's sleep and then hopefully I will be much better tomorrow."
His team manager Daniele Romagnoli said Yamaha needed to give Lorenzo more grip from the rear of his bike.
"Today we didn't quite make the good start that we've maybe become used to lately, plus Jorge wasn't feeling very well; he was quite weak which made his job much harder," said Romagnoli.
"The main problem is on the rear, we don't have enough grip on the entry to the corner or under acceleration and at this track these areas are particularly important."
By contrast Rossi was delighted with his day's work, having topped the times for most of practice.
"Today we made a great start," said the championship leader. "We were concentrated and strong and I am really happy to start in front here at Phillip Island, which is somewhere that I love to ride.
"We were able to get a lot done in the practice session and try many different things and I was able to ride just how I wanted to."
He also warned that there was even more speed to come.
"We can definitely improve more - even though we already have a good pace we will continue to work tomorrow and try to find a little bit more, but for the first day I think we can be very happy about our work," said Rossi.