After a dry opening day at the first official World Superbike test of 2011, rain on Thursday produced two wet track sessions at Portimao - which ended with Jonathan Rea going fastest on his final lap.
Rea lost out on a clean sweep of Wednesday's dry sessions when he was knocked from the top at the last moment by Jakub Smrz, but it was the Castrol Honda rider who was on the attack in the closing stages of Thursday.
Like half of the 16 riders present, the British star sat out the morning session completely - and he only rode for 14 laps in the afternoon. But that was enough to climb quickly up the order and replace Carlos Checa in P1 with a little over ten minutes to go.
Former MotoGP star Marco Melandri, just 15th on day one, then fired his factory Yamaha ahead with just one minute remaining and it took a last lap attack from Rea to reclaim the top spot by 0.345sec.
Rea's best lap was a 1min 54.718sec, which compares with the dry best by Smrz of 1min 43.503sec.
“Today was a bit grim at the start so we sat out the first session hoping it would dry but it didn't,” declared Rea. “We ended up taking to the track in the last hour and to my surprise we found our wet base setting very good as well. It was puddles, wet and damp wet, but a decent day anyway.”
Melandri, a MotoGP race winner in the wet, rode in both Thursday sessions for a total of 33 laps, an amount beaten only by Supersonic Ducati's Maxime Berger (43).
Checa, fifth in the dry on day one, had enjoyed a near two-second advantage over Melandri's team-mate Eugene Laverty at the end of the morning session, but the Althea Ducati star didn't improve in the afternoon and dropped to third place (1.444sec from Rea) as a result.
Another known wet weather talent, Sylvain Guintoli, finished the day fourth overall, one place ahead of new Liberty Ducati team-mate Smrz. Tom Sykes was the only Kawasaki rider on track on Thursday and finished in sixth.
Rookie Laverty didn't ride during the afternoon and slipped down the timesheets to seventh overall.
Noriyuki Haga (PATA Aprilia) did ride in both sessions, but his best was only good enough for eighth, 3.6sec from Rea. Ayrton Badovini was the top BMW Italia rider in ninth, with Michel Fabrizio tenth after an afternoon fall from his Alstare Suzuki.
Badovini's team-mate James Toseland and Berger were the last of the twelve riders to record a lap time.
Four riders didn't complete a lap on Thursday: Reigning world champion Max Biaggi (who sat out the morning then headed to Monaco for an important PR appearance) and his factory Aprilia team-mate Leon Camier, plus Rea's team-mate Ruben Xaus (who already has three wet days of testing under his belt) and new factory Kawasaki rider Joan Lascorz.
Testing at Portimao concludes on Friday evening.
A second official pre-season test will be held at Phillip Island, Australia, on February 21-22. The first round of the new season takes place at the same track on February 27.