Takuma Sato marked his return to Formula 1 with a bang - as he staked his claim to a race seat with Scuderia Toro Rosso in 2009 by impressively topping the first day of winter testing in Barcelona, even if the Faenza-based squad insisted that little could be read into the final pecking order.

With all teams bar Toyota and 17 drivers in action around the Circuit de Catalunya, lap times were clouded somewhat by the fact that some ran their 2008 cars whilst others wheeled out an interim 2009 version.

STR stuck to their 2008 mount and Sato made good use of it to head the timing screens, just over four tenths of a second faster than the second-placed driver, his fellow auditionee for a seat at the Red Bull 'junior' outfit, GP2 Series front-runner S?bastien Buemi. The duo covered respectively 121 and 117 laps of the Montmel? track as they helped the team to assess the slick tyres that will make a welcome return to the top flight in 2009.

Both drivers completed their low-downforce runs on Bridgestone's softer-compound rubber without committing any mistakes and turning in consistent lap times, and whilst Buemi will remain in the car all day on Tuesday, Sato will hand over at lunchtime to 2008 incumbent S?bastien Bourdais.

Buemi ended up just over a tenth of a second clear of third-placed Alex Wurz in the Honda, with GP2 front-runners and F1 aspirants Bruno Senna and Lucas di Grassi some way further down the order in 15th and 17th positions respectively as they duel it out for potentially the second berth at the Brackley-based concern next year. Senna completed fewer laps of the pair, but wound up the quicker by more than a second in their internecine battle to impress.

Experienced hand Wurz, for his part, spent his time evaluating various aerodynamic components for next season and running the Bridgestone Potenza slick tyres. The Austrian will hand over to regular driver Jenson Button on Tuesday for the remainder of the test.

"The view from the cockpit is just so much nicer with slick tyres on the car!" the former Benetton and Williams ace joked. "As a driver I prefer the driving style with slicks, so I am happy that the change has finally come, even if it is too late for me to race with them.

"My focus for today was on gathering information with the tyres whilst running various 2009 downforce levels. We have come away with good answers and a clear direction, so I am pleased with the work that we achieved.

"It was nice to see the two young guys in action with Honda today. Both understood the car very quickly, but how they develop from here with a full day in the car will be important."

Fourth and fifth-quickest on the end-of-day timesheets were the two McLaren-Mercedes' of test drivers Pedro de la Rosa and Gary Paffett, the pair winding up just over half a second apart after completing respectively 65 and 78 laps in cars fitted with slick tyres and modified to simulate 2009 levels of aerodynamic downforce. De la Rosa focussed on the KERS-equipped MP4-23K, whilst Paffett will run solo on day two.

Luca Badoer was sixth-fastest for Ferrari just behind Paffett, as the Prancing Horse echoed McLaren's programme of low downforce and slick rubber, with weights added to the cars to simulate the situation when KERS will be employed. The Italian tried out new components and began a lengthy engine and gearbox reliability programme that took up the entire day, whilst fellow tester Marc Gen? concluded 13th-quickest in an unmodified F2008 as he looked at set-up options, covering just 33 laps to Badoer's 108. Both drivers will take to the circuit once again on day two.

Next in the running order was Robert Kubica in the BMW-Sauber, both the race-winning Pole and the Munich and Hinwil-based outfit's test driver Christian Klien driving interim F1.08B machines featuring a modified 2008 chassis with some of the bodywork complying to the 2009 regulations, with the latter's car also equipped with BMW's own KERS device. Both drivers experimented with different mechanical and aerodynamic solutions.

"We are gaining more and more experience with the KERS system," commented tenth-placed Klien, who will relinquish the wheel to race driver Nick Heidfeld on day two, before taking over again from Kubica on the final day. "We still have a lot of work to do to fine-tune the system, though."

Five-time consecutive World Rally Champion S?bastien Loeb lapped an eye-catching eighth-quickest on his maiden 'proper' run for Red Bull Racing, the Frenchman less than two tenths of a second shy of Kubica's best effort. Loeb has been invited to test by the energy drinks-backed squad as a prize for his record-breaking title success, and clearly demonstrated the benefits of his Silverstone shakedown run last week.

After spending most of the morning settling in and finding a good balance on the car, the 34-year-old was actually put to more 'serious' use in the afternoon, when he worked on evaluating Bridgestone's 2009-spec slicks and providing the team with valuable data. RBR new boy Sebastian Vettel will take over for the final two days.

Behind Loeb, the recently re-confirmed Nelsinho Piquet placed ninth for Renault as he concentrated on 2009 set-up and tyre work, and the Brazilian was joined by 23-year-old Giedo van der Garde, who drove the R28 for the first time as a reward for his World Series by Renault title success. The Dutchman completed 32 laps as he acclimatised to the car and adapted well to his new surroundings.

"It was a constructive day," affirmed Piquet, "although obviously we are right at the very start of winter testing and the cars will be very different next year. Still, it's nice to get a feel for how things are going to be with the sort of set-ups we will be running next year and with slick tyres. The car felt quite different today with these new settings, but the track conditions were good, which helped us."

"It was a great day," enthused former Spyker F1 test driver van der Garde. "The last time I was in a Formula 1 car was over a year ago, so I had to get used to the speed of the car again.

"We improved every time we went out, working on getting a better set-up, and hopefully we can continue like this tomorrow morning. It's been nice to work with the team - they are a good bunch of people and I'm really enjoying the experience."

"It's nice to be back testing again after a break," summarised the R?gie's chief test engineer Christian Silk, "and obviously with new rules coming into force next year it's going to be an interesting winter test period. We had a good first day of the programme with no major problems, and we learnt what we needed to as we worked on 2009-type set-ups with slick tyres.

"Giedo had had a good first day with us; he has limited experience of Formula 1 and so it was a learning process, but it was a positive session and he worked well with the engineers. We'll debrief with him tonight and give him another run out tomorrow morning."

Behind Piquet, Williams test driver Nico H?lkenberg wound up eleventh, the 2008 F3 Euroseries king encountering no problems as he covered 116 laps in the Grove-based concern's interim FW30 ahead of his hand-over to namesake Nico Rosberg.

Force India duo Vitantonio Liuzzi and Adrian Sutil, meanwhile, proved evenly-matched both in terms of laps covered and times on the stopwatch in twelfth and 13th spots respectively, with Gen?, Senna, van der Garde and di Grassi completing the order at the close of day one.

To see the testing times in full, click here