Lewis Hamilton helped McLaren set the fastest time of the 2009 cars during the final day of this week's test at Jerez in Spain on Friday.
Although Sebastian Bourdais was guaranteed the top spot as his Scuderia Toro Rosso outfit were alone in running their 2008 car, it was left to Hamilton and Renault's Fernando Alonso to lead the way with the new cars.
Hamilton's best lap of one minute 19.632 seconds, set with his McLaren fitted with a 2008 rear wing, was just more than two tenths of a second clear of Alonso, who appeared to eek some more pace from the R29 than it has shown capable of earlier in the week.
Alonso seemed relieved to have delivered some of his new car's potential, with the team having had a fairly frustrating early experience with the new car.
"After doing so many laps with the car yesterday, we concentrated more on set-up work today to get a better understanding of the car and make it easier to drive," said the Spaniard.
"Overall, we have to be very happy as we managed to do lots of laps and the car responded well to the set-up changes we made, so I think we've found some good solutions.
"Every day the driveability of the car is improving and although we still have a lot of work to do before the start of the season, we are definitely moving in the right direction."
Nico Rosberg was fourth fastest for Williams, almost one-and-a-half seconds adrift of Alonso, while Mark Webber was fifth for Red Bull Racing.
The Australian's morning was blighted by a mysterious mechanical problem and he later brought out the only red flag of the day when he stopped on track near the end of the day. Nevertheless the team were encouraged by the first week's running of the new car
RBR's Head of Race Engineering Ian Morgan said: "Apart from a few minor niggles, which are to be expected with a brand new car, this first test has produced pleasing results. RB5 proved to be generally reliable and its performance seems encouraging straight out of the box."
Kazuki Nakajima was the only other runner, completing a total of 34 laps but he was focusing on pitstop practice so he did not record an official time.
Pos Driver Team Time Laps
1. Bourdais Toro Rosso-Ferrari (B) 1:17.472 117
2. Hamilton McLaren-Mercedes (B) 1:19.632 94
3. Alonso Renault (B) 1:19.846 109
4. Rosberg Williams-Toyota (B) 1:21.217 70
5. Webber Red Bull-Renault (B) 1:20.738 92
6. Nakajima Williams-Toyota (B) No time 34
All Timing Unofficial