Brazilian Bruno Senna, nephew of the late triple world champion Ayrton, made his test debut for Honda in a new-look Formula One at Barcelona's Circuit de Catalunya on Monday.
With cars running on slick tyres and using very different-looking rear wings in preparation for next year's rule changes, teams began their first official test since the championship ended in Brazil on Nov. 2.
McLaren's Lewis Hamilton, the 23-year-old Briton who became Formula One's youngest champion at Interlagos, was absent as the attention turned to those hoping to join him on the starting grid next season.
Senna, the 25-year-old who finished runner-up in the GP2 support series this year amd could replace compatriot Rubens Barricello at Honda, completed 39 laps and was only 15th fastest of the 17 drivers in action on a cold but dry day.
"The first day of my first Formula One test has been just as big a moment as I expected it to be," he said in a team statement.
"I was feeling quite calm but on my first lap out of the garage I realised the significance of the moment. This is a very special opportunity and one which has been a dream my whole life.
"The team were great and left it to me to find my level, but by the end of my second run I was feeling very much at home in the car," added Senna, whose uncle won all his titles in Honda-powered McLarens.
Japan's Takuma Sato, who last raced for now-defunct Honda-backed Super Aguri at the Spanish Grand Prix in Barcelona last April, did his comeback hopes no harm by topping the timesheets for Toro Rosso in an unofficial one minute 20.763 seconds.
Switzerland's Sebastien Buemi, the Red Bull test driver who is also hoping to fill the Toro Rosso seat vacated by Germany's Sebastian Vettel, was second fastest for the Ferrari-powered team in 1:21.071 with Honda test driver Alexander Wurz third.
Sato's time was a second quicker than Kimi Raikkonen's pole position of 1:21.813 at this year's Spanish Grand Prix, and only marginally slower than the quickest practice lap for that race, but Toro Rosso played down the significance.
"Testing times are always hard to evaluate, but today there was probably a bigger discrepancy between the car configurations used by the teams," the team said in a post-session report.
"For our part, the only concession to the new 2009 aerodynamic rules was to run with less downforce."
McLaren had Spanish test driver Pedro de la Rosa and Britain's Gary Paffett in action while champions Ferrari, running an engine and gearbox reliability programme, were present with testers Luca Badoer and Spaniard Marc Gene.
The regulars were also joined by Citroen's world rally champion Sebastien Loeb, taking part in a full test session for the first time after winning his fifth title in succession.
The Frenchman, appearing for Red Bull who also sponsor his rally team, was a highly impressive eighth in front of Renault's race driver Nelson Piquet and Force India's Adrian Sutil.
Piquet was joined at Renault by 23-year-old Dutchman Giedo van der Garde, earning a test for winning this year's World Series by Renault title.