Jenson Button set the fastest time in morning practice at Barcelona as Formula One enters the final week of testing before the new season begins.
Button set a time of 1m 23.510 in his McLaren and using the hard tyres, three tenths ahead of Sergio Perez's Sauber using the softer medium compound tyres and a further tenth ahead of Roman Grosjean in the Lotus after a warn and dry morning at the Catalunya circuit.
The British 2009 World Champion completed just 27 laps in the four-hour session - with much of the first hour spent practising pit stops with his team, while his rivals clocked up between 40 and 60 laps each. Vitaly Petrov in the Caterham clocking up 63 laps - roughly the equivalent of a full Grand Prix.
The Russian driver was not expected to drive for Caterham until Friday, but team mate Heikki Kovalainen fell ill with food poisoning overnight.
The Caterham was a full 23 km/h (14mph) quicker than Button's McLaren in the speed trap, but almost 1.5 seconds off the Brit's lap time, showing clearly how valuable downforce is at the Spanish circuit.
The field of 10 drivers was separated by just two seconds as they broke for lunch, suggesting that all teams are on similar testing strategies.
Out-right performance is almost impossible to judge from these test sessions, but it is worth noting that Mark Webber in the Red Bull finished the morning fifth fastest with a time of 1m 23.993 and Felipe Massa posted a time of 1m 24.328 which put him eighth overall.
The first race of the season is on 18 March from Albert Park, Melbourne.