Dani Pedrosa had finished Monday's Qatar test just 0.064sec behind new Repsol Honda team-mate Casey Stoner, but a tyre problem during Thursday practice for the grand prix saw the difference increase ten-fold.
The Spaniard was still second best behind the Australian, but his pace got significantly slower each time he went back out on track.
On his first run Pedrosa set his best lap time of the session, a 1min 56.362sec - which would be 0.6sec slower than Stoner's eventual best.
But on his second run Pedrosa couldn't get lower than a 1min 57sec, and by his third and final run the 2010 title runner-up was unable to improve on 1min 58sec.
"I had a problem with the rear tyre that we need to understand,” he said. “It's the first issue we've had this winter with the tyres, so I hope it's an exception to the rule.
“We started the practice very well, we were fast in the first exit and then we stayed with the same tyre, the softer compound, for the whole session. Even if I used the same compound during the winter test without any problem for several laps, today already in the second round I felt it dropped down a lot, and in the third and last one it was even worse.
“With only 45 minutes practice, the rounds are very short and you don't have much time to make changes. Maybe the tyre had a problem, maybe it dropped down a lot because with 125cc and Moto2 bikes on track the conditions were very different comparing with the test of few days ago, we don't know exactly.
“Anyway, the grand prix weekend just started and we will try with another tyre tomorrow to understand more. I hope we can take the best profit of both practices sessions to prepare for the race in a good way.”
Third Repsol Honda rider Andrea Dovizioso was eighth quickest. The Italian also has issues to fix.
“With four days of practice it is important to manage the tyres so today we used only the hard compound to save the soft tyres for tomorrow and the coming days as I expect it will only be possible to use the soft rear tyre for the race,” he began.
“The biggest problem today was a vibration on the front when I released the brake and this limited me a lot because I was not able to push and lean as I wanted. We need to understand this problem and solve it as soon as possible.”