Mercedes' Nico Rosberg was the fastest driver during Formula One preseason testing Tuesday, while Fernando Alonso took a long first spin with Ferrari's new car for 2013.
Defending champion Sebastian Vettel of Red Bull had the best time until late into the afternoon session when Rosberg unleashed a flying lap of 1 minute, 22.616 seconds. Vettel's one-lap time ended up being the fourth fastest of the day.
"We had a mixed day today with some laps lost this morning. However, we were able to work through a good programme this afternoon and, of course, it's always nice to be quickest at the end of the day," said Rosberg, who is teaming up with newcomer Lewis Hamilton this season.
Rosberg had to cut short his morning run after 14 laps because of a problem with his car's gearbox. He was able to continue after lunch and get in 54 laps on the day.
"The car, compared to last year, has a much better base. It rides lower, the aerodynamics are better, the platform is better. It feels a lot stronger. It's faster," Rosberg said. "It's a pleasure to drive."
Kimi Raikkonen followed suit in his Lotus to beat Vettel's initial pacesetting effort for the day's second quickest time. The Finn was followed by Alonso with the third-best lap in his first drive with Ferrari's F138 after he sat out testing in Jerez.
"It wasn't an ideal day in terms of the number of laps we completed, but the car feels strong and we have made some good progress," Raikkonen said after finishing 44 laps on the day.
Alonso was the only driver to do more than 100 laps with 110.
The Spaniard was cautiously optimistic about the car following his first few hours behind the wheel, saying that it was practically the same vehicle that he took to within three points of the title last season.
"The car is the same as last year until we put in the changes before Melbourne, when we hope we will close the gap with the leaders," Alonso said, referring to the car's lack of pace that dogged it in 2012.
"There are no surprises now, unlike last year we were at a loss (to start the season). We still need to improve the car because at the end of last season we were quite far from Red Bull, McLaren, and Lotus."
Alonso said that the Pirelli tires for this season provided better grip early, but then suffered a quicker degradation, meaning that he foresees more pit stops this season.
The day was incident-free with only two short red-flag stoppages due to Esteban Gutierrez's Sauber running out of gas and a temporary problem for Charles Pic's Caterham.
Williams started the opening day of testing in northeastern Spain by launching its FW35 race car for this season. Maldonado recorded the fifth fastest lap and the second most laps with 86.
The British outfit was the last to present its car of the 11-team field.
Testing will continue in Barcelona through Thursday, with a final test next week before the season-opening Australian GP on March 17.