JEREZ, Spain (AP) - Sebastian Vettel posted the fastest lap for Ferrari on the first day of pre-season Formula One testing, while last year's championship runner-up Nico Rosberg clocked a massive 157 laps.
Rosberg lost out on the title to Mercedes teammate Lewis Hamilton in a gripping and often tense tussle last year that went down to the final race in Abu Dhabi.
"Today every lap counts, I can feel I'm rusty," Rosberg said. "I'm definitely not as good now as I was on Sunday in Abu Dhabi. So I need to use these days to get back up to speed."
The season opens March 15 in Melbourne, and if Sunday's testing is anything to go by, Rosberg is in the mood to upstage Hamilton.
"I want to become an even better driver this year," Rosberg said. "That's my aim and my personal challenge and it's a great challenge."
The German driver was so keen to pile on the laps he even had lunch sitting in his car.
Vettel's best lap of 1 minute, 22.62 seconds was .157 quicker than Swedish driver Marcus Ericsson and .486 better than Rosberg.
There are four days of testing. Hamilton drives today and Wednesday.
Daniel Ricciardo was fourth fastest - .716 behind - and completed 35 laps in his Red Bull.
The long session was interrupted twice, with the red flag coming out for the second time when Carlos Sainz Jr stalled his Toro Rosso.
Testing continues until Wednesday.