The four-time world champion, who switched to Ferrari from Red Bull over the winter, completed 60 laps in the new SF15-T, setting a best time of 1m 22.620s in the afternoon session to go clear of the field.
“Today was a good start," commented Vettel. "I can’t say more than that, because this is only the beginning. Everything is different, even the philosophy behind the car, when compared to what I was used to. But I immediately felt at ease within the team and the guys gave me a very warm welcome."
The second-fastest time of the day went to Sauber’s Marcus Ericsson who, like Vettel, was making his first appearance for his new team. The Swede, who completed 73 laps, took his blue and yellow C34 round in 1m 22.777s late in the day to demote early pacesetter Nico Rosberg to third.
“I think we have good reasons to be happy,” said Ericsson. “We were able to complete a lot of laps, and we went through quite a few different small tweaks on the set-up and did all the installations needed. There were no major problems with the car, which was really the main thing.”
Dropping a position would have mattered little to Rosberg on a day when reigning champions Mercedes demonstrated ominous form. Having shaken down the F1 W06 Hybrid at Silverstone last week, the German clocked up a remarkable 157 laps in the freshly-unveiled car - a tally more than twice that managed by any other team.
“That was a great start to the winter testing,” Rosberg commented. “In the beginning it’s all about reliability and we managed to do a lot of mileage today. The guys in the factories built a complete new car and now we come here and it’s working great, so the team did a fantastic job over the winter.
“I was able to do some good long runs on the first day and that’s really amazing. We have such a great team and this is what makes me really happy. As a driver, you always want to find out how quick you are compared to the others - but that will have to wait until qualifying in Melbourne. The next testing days are all about making sure we know the car inside out and we’ve made a good start with that today.”
Daniel Ricciardo was fourth-quickest in Red Bull’s uniquely liveried RB11, though mechanical issues restricted the Australian to just 35 laps. Still, Ricciardo said the new car already felt like a step up on the RB10: "I won’t go into too much detail but it’s there. We didn’t do a whole lot of laps but definitely more than at this test last year!
“In general everything is behaving as it should. Obviously we had a couple of issues, but once the car is running it’s all going pretty normally.”
Williams were late to join proceedings, but eventually completed a useful 73 laps and set the fifth-fastest time with Valtteri Bottas at the wheel of the FW37.
"The car was consistent, so it’s a really good start to the week and we are pleased that it’s still a step up from the car we had at the end of last season," said the Finn. "We know we have a lot to learn and improve, but we also know where these gains can come from, and have work to do with the car performance and the power unit. There are a lot of strengths in this car and we’ve made good progress in just one day, so I am very pleased."
Marginally slower than Bottas was Carlos Sainz Junior who recorded the sixth-quickest time as he gave Toro Rosso’s STR10 its maiden outing. However, it proved to be a rather stop-start day for the Spanish rookie who caused the session's second red-flag stoppage when his car came to a halt on the back straight late on.
The times were rounded out by Fernando Alonso who managed just six laps in McLaren's new Honda-powered MP4-30. The Spaniard did complete one timed effort, though it was a full 18 seconds off the leading pace.
“Given the complexity of modern Formula One machinery, the sorts of issues we encountered today weren’t too surprising," said the Spaniard. "They’re just the things you experience on the first day of a Formula One test. But it’s been a fantastic day for me: to have the privilege to drive the car for the first time - for the comeback of McLaren and Honda after 23 years - makes me feel extremely proud.
“Obviously, I don’t really have a feeling for the car yet - I only did a handful of laps, and most of those were at slow speed, conducting preliminary checks - so I need a bit more time to be able to speak accurately about it. But everything seems to be responding well, and showing us what we expected."
Absent from the timesheet were Force India, who have opted to skip the first test completely, and Lotus, whose car only arrived in Spain late on Sunday. The Enstone-based team say the E23 Hybrid is now undergoing its build programme and is not expected to run until the third day of the test on Tuesday.
Unofficial Sunday testing times from Jerez:
1. Sebastian Vettel, Ferrari, 1m 22.620s, 60 laps
2. Marcus Ericsson, Sauber, 1m 22.777s, 73 laps
3. Nico Rosberg, Mercedes, 1m 23.106s, 157 laps
4. Daniel Ricciardo, Red Bull, 1m 23.338s, 35 laps
5. Valtteri Bottas, Williams, 1m 23.906s, 73 laps
6. Carlos Sainz Jr, Toro Rosso, 1m 25.327s, 46 laps
7. Fernando Alonso, McLaren, 1m 40.738s, 6 laps