Piquet, whose father and namesake was a triple world champion, led his Finnish team mate Heikki Kovalainen by just over a 10th of a second in only his second day of testing with the team.

"This was another day of learning and improving for me," said Piquet in a statement.

"The more laps I do, the better things are getting and I feel like I am improving with every run."

Piquet has joined Renault as a test driver for 2007 after finishing runner-up in the GP2 championship that acts as a feeder series for Formula One.

The man who beat him to the GP2 title, 21-year-old Briton Lewis Hamilton, had his first full day of testing with McLaren and was sixth fastest.

"It is a steep learning curve and as a result I am making sure I get the most out of my time with the test team and engineers," said Hamilton.

The Briton is in the frame to replace departing Kimi Raikkonen alongside world champion Fernando Alonso at McLaren next season.

The man considered his main rival for the job, Spaniard Pedro de la Rosa, was third fastest after focusing on tyres and set-up programmes for the next two races in China and Japan.