McLaren’s Jenson Button set the early pace on the final day of the second pre-season test.
After two hours’ running at Barcelona’s Circuit de Catalunya, the 2009 world champion was 0.721 seconds quicker than Kamui Kobayashi’s Sauber.
The Toro Rosso of rookie Jean-Eric Vergne was third fastest ahead of Paul di Resta’s Force India.
Ten of the 12 teams are in Spain preparing for the first race of the season in Australia on 18 March.
World champions Red Bull are widely considered to have the fastest car, but testing is a notoriously unreliable guide to form at the first race.
That is because lap times are sensitive to tyres and fuel loads and it is impossible to know the specification in which the teams are running the cars.
McLaren have a major update to come on their car at the final pre-season test, which starts at the same track on 1 March.
Button said after Thursday’s testing:
“We’ve done a lot of reliability work over the past three days – more than 100 laps on each day.
Most of that has been longer runs, getting used to the feeling of the car over a long run and set-up work for the longer runs.
“We’ve also been really working hard to understand this year’s Pirelli tyres and getting the car to work efficiently around them. That’s a key part of the programme this winter.
“There are a lot of cars out there that look competitive, so we’ll keep pushing. We should hopefully bring our upgrade package to the next test and that will see us through to the first race in Melbourne.”
Ferrari have been playing down their car’s performance, and it is especially difficult to read their form as, unlike McLaren and Ferrari, they have so far not done any race-distance runs.
Also running on Friday are Pastor Maldonado in the Williams, Heikki Kovalainen in the Caterham and Nico Rosberg in the Mercedes.