Nicky Hayden was quickest in each of Friday's practice sessions at a rainy Valencia, the scene for the final round of the 2008 MotoGP season this weekend.
The American rider, the world champion in 2006, is preparing for his last race with Repsol Honda before joining Marlboro Ducati for 2009, and set the overall best time of the day with an effort of one minute 45.777seconds.
Hayden was joined at the top of the timesheets by team-mate Dani Pedrosa, who is looking to make it a Valencia double following on from his triumph at this circuit 12 months ago.
The Spaniard trailed Hayden by less than a tenth of a second, while Fiat Yamaha's Jorge Lorenzo was a further tenth back in third place, just ahead of team-mate and recently-crowned world champion Valentino Rossi.
Heavy rain in the morning curtailed the six-time champion's running in the opening session, while a lowside crash midway through the afternoon laps also compromised the Italian.
"Today was a difficult day because this track is quite bad when it's wet and cold like this - the asphalt really doesn't give enough grip," said Rossi.
"This morning I went out just when it started to get really heavy and so I wasn't able to do any good laps, but this afternoon was better.
"Unfortunately I had a small crash at the last corner when I made a mistake and lost the rear, but I wasn't hurt at all and I was able to go back out with a slightly harder tyre and continue to work."
Ducati's Casey Stoner was fifth quickest, while Andrea Dovizioso (JiR Team Scot), Randy de Puniet (LCR Honda MotoGP) and Sylvain Guintoli (Alice Team) completed the top eight.
Guintoli's day was soured, however, when he picked up a leg injury after a heavy crash.
Colin Edwards was ninth and Shinya Nakano (Honda Gresini) 10th, while Edwards' Tech 3 Yamaha team-mate, Britain's James Toseland, struggled in the low-grip conditions and could manage only 16th.
Toseland said: "It was a tough day and we've got to find something to improve because the forecasts are for more rain tomorrow, and I need to find a bit more from the bike.
"I just didn't have a very good feeling and I'm not happy, but I've got some ideas."