Fernando Alonso and Renault continue to prove the outstanding pace of the R26, as they topped the timesheets at Jerez.

The Spaniard, who was joined by test driver, Heikki Kovalainen, posted the quickest time set by a V8 powered car this year, just 0.447s off the time posted by Pedro de la Rosa in the V10 McLaren in mid-January.

Fernando concentrated primarily on tyre development and set-up work in order to learn more about the R26's handling characteristics.

Meanwhile, Kovalainen successfully completed a race distance this morning, but was then forced to stop running following a problem with the rear wing. The team chose not to take any risks in the interests of driver safety, and the part in question was sent back to Enstone immediately for analysis and to enable modifications to be made as quickly as possible. The team is working hard to get modified components to Jerez for the end of the week, but quality remains paramount; should they not be available in time, they will be used next week in Valencia.

While waiting for new components to arrive, the team will run with a single chassis tomorrow, with Giancarlo Fisichella and Heikki Kovalainen sharing seat-time in the R26.

"We had an interesting day of testing," said Alonso. "We concentrated on the tyres again, which are going to be a very important factor this year, and worked on chassis set-up. The gains we made were good in terms of improving the grip and balance of the car. Now, we need to carry on working and see how things go – it is hard to say more than that at this stage, but the main thing is that we concentrate on our programme."

"I managed to do another race distance today, which was good," added Kovalainen. "The car handled well and I felt comfortable at the wheel again. We then had the problem with the wing that meant I had to stop running, but the main thing is that we will still be able to carry on running tomorrow."

"We managed to get through a large part of our testing programme today," said Christian Silk, the French outfit's chief test engineer. "Heikki completed another race distance, while Fernando worked on software this morning as he waited for track conditions to improve. He then focused on tyre development and chassis set-up, and we found some interesting ideas to explore further. Overall, it was a positive day in spite of the problem with the rear wing this afternoon."

Honda continues to give the French team a run for its money, with Jenson Button and Rubens Barrichello finishing second and fifth quickest. The Englishman ran through a tyre evaluation programme, completing 17 laps in the morning session and a further 41 laps in the afternoon.

The Brazilian lost much of the morning as a result of a technical problem, however, later he was able to resume and worked through a chassis set-up programme, completing a total of 60 laps over the course of the day.

McLaren will be delighted with the performance of the 'new' Mercedes powerplant, which made its debut today. The job of running the new engine was entrusted to Juan Pablo Montoya, who didn't take to the track until 13:30. By the end of the session the Colombian, whose programme focused on set-up work and various component evaluations, had finished 53 laps, posting the third fastest time of the day.

Following its first run, a McLaren source told Pitpass that the new engine was; "better, faster and more reliable" than its predecessor.