French driver Romain Grosjean handed over to Lotus team-mate Kimi Raikkonen after setting the fastest lap on the track so far in Formula One's first pre-season test.
The Frenchman, who endured a crash-prone first full season last year, completed 95 laps with a best time of one minute 18.218 seconds in the Spanish sunshine.
On a day when rivals Mercedes completed just 15 laps, with Lewis Hamilton crashing into the tyre wall after the brakes on his car failed, the Renault-powered Lotus went around the circuit without any drama.
"It was good today; the programme went to plan and we showed we have good reliability. For me, the whole test has gone well which bodes well for the year ahead," he said.
"Even if it doesn't mean anything during testing, it's still good to be at the front."
Raikkonen, the 2007 champion with Ferrari who finished third in the championship on his comeback with Lotus last year, will be in the car for the final two days on Thursday and Friday.
Australian Mark Webber pounded around for 101 laps, more than anyone else, in the new Red Bull RB9 to take his tally to 174 over the two days.
His was the fourth fastest time on another solid day for the world champions.
"I think in terms of consistency it's great," he said of the new RB9. "I'm very happy with the car and myself... overall it's been very good. The car gives me the confidence to push pretty hard and that's always an indication that you have something you can build on."
Triple world champion Sebastian Vettel will take over the testing duties from Thursday.
Britain's Paul Di Resta was second fastest in the Force India with Australian Daniel Ricciardo third for Toro Rosso, even if nobody was paying too much attention to the timesheets.
Ferrari's Felipe Massa was eighth, a place behind Mexican Sergio Perez who was making his test debut for McLaren after his move from Sauber.
"Today, we concentrated 100 percent on the aerodynamic side and on the exhausts," said Massa, who used the morning to do aerodynamic tests and constant speed runs rather than trying to set a 'flying' lap.
"All the changes to the car took longer than planned, but in the afternoon, I managed to do three long runs which were very important in order to understand which direction we need to follow in the coming days," added the Brazilian.
Marussia had new Brazilian signing Luiz Razia testing their car for the first time although an engine problem limited his track time in the afternoon.