New McLaren driver Sergio Perez set the fastest lap on the second day of Formula One testing at Barcelona's Circuit de Catalunya on Wednesday.
The Mexican, who has moved from Sauber to replace 2008 champion Lewis Hamilton at the team, completed 97 laps - nearly one-and-a-half times the Spanish Grand Prix race distance - with a best time of one minute 21.848 seconds on the soft tires.
Perez did a series of shorter runs in the morning and then longer ones in the afternoon focusing on familiarizing the driver with systems and procedures including the cockpit switches and radio messaging.
Red Bull's triple world champion Sebastian Vettel had been the fastest before lunch, although testing times must be treated with caution since teams are working through different programs, but was forced to end his session early.
"We had some issues with reliability today and we couldn't do as many laps as we wanted," said the German, who was still second fastest overall (1:22.197) and did 84 laps. "It was nothing disastrous, just small things that hampered us today."
The team's race engineering coordinator Andy Damerum said the problems would be resolved by the start of Thursday's session with Australian Mark Webber.
"The stops we had today weren't too serious...we know where the issues are," he added.
Kimi Raikkonen was third on the timesheets for Lotus (1:22.697) although the 2007 champion was sidelined for much of the morning and part of the afternoon by a gearbox problem.
Hamilton, now with Mercedes, was fourth fastest in 1:22.726 after completing a whopping 121 laps - the most of any driver - with his best lap set on the hard tires in the morning.
"We had a good day and it was nice to get so many laps in," said the Briton. "We're making continual steps forward in terms of our understanding of the set-up and the tires.
"The guys are working really hard both here and at the factory and it's encouraging to see the amount of work that's being put in. We're focusing on our own program and just getting on with it."
Ferrari's Fernando Alonso was fifth fastest.
The second test of the pre-season ends on Friday. The first race is in Australia on March 17.
(Reporting by Alan Baldwin, editing by Alison Wildey)