Fernando Alonso drove Ferrari's new Formula One car for the first time in Barcelona on Tuesday and said it was on another planet compared to the tricky one he wrestled into title contention last season.
The Spaniard, ending a long absence from the cockpit, clocked the third fastest time in testing at the Circuit de Catalunya.
The 31-year-old, runner-up to Red Bull's triple champion Sebastian Vettel last year, had skipped the first pre-season test in Jerez to focus on his physical preparations for the season starting in Australia on March 17.
With the team declaring his training workouts in the gym and on the road to have been "worthy of the best Olympic athlete", Alonso completed a total of 110 laps in the F138 with a best time of one minute 22.952 seconds.
"I feel reasonably pleased with this first day and I can say I share (team mate) Felipe's (Massa) opinion that the car is on another planet compared to the one we began with on the first day of testing last year," said the double world champion in a team release at the end of the session.
Alonso said the target was to work on reliability, aiming to complete more than 100 laps each day, before focusing on performance in the final test.
"I knew from looking at the Jerez data what sort of car I would find here today, as in fact we know more or less what we will see at the first race in Australia, in terms of what new parts we will have and how many tenths they will produce," he said.
"This is down to all the work done over the winter in the wind tunnel and the numerous tests which confirm the parts that are on their way will give the expected results."
Mercedes's Nico Rosberg was the fastest driver on track on an overcast but dry day that turned brighter later, lapping in 1:22.616 and just quicker than Kimi Raikkonen in the Lotus (1:22.623).
Rosberg was sidelined for a while by a gearbox problem after 14 laps and ended up completing 54.
"It's always nice to be quickest at the end of the day. In general I feel happy and comfortable in the car and it feels better than the last time we were here at this track," said the German.
Raikkonen did 44 laps, the lowest tally of any driver, with the team suffering telemetry issues that limited their track time.
Vettel was fourth fastest for Red Bull in 1:22.965 with Venezuelan Pastor Maldonado, winner of last year's Spanish Grand Prix, fifth on the timesheets in the first run for the new Williams.
"The FW35 feels like we have made a real step forward. There is still a lot to discover with the new car but this is a good starting point for us for the season," said Maldonado.
Red Bull said Vettel had been hampered early in the day by a software issue but the champion was top of the timesheets for much of the afternoon.
"It's very important for us to put good mileage on the car and this morning that wasn't really possible," said the German.
"We had a small software issue this morning, I think many teams had. That wasn't ideal but we got it fixed and after that it was another decent day."
(Reporting by Alan Baldwin, editing by Tony Jimenez)