Nine stars from the current Formula 1 grid will drive in this week's two-day post-race session at the Circuit de Barcelona-Catalunya, with nine teams also devoting time to test drivers - Mercedes are the exception, having chose to use their 2018 race line-up.
Bottas posted a 1m16.904s to lead the way on the supersoft compound tire, a lap time that would have been good enough for seventh on the grid in Sunday's Spanish Grand Prix on the same tire.
Mercedes showed dominance throughout the entire weekend of the Spanish Grand Prix, the fifth race of the 2018 Formula 1 season, by placing Lewis Hamilton in first place in every timed session for the weekend.
The remaining laps saw Bottas nurse his wheels which he had used for more than two thirds of the race to the finish line.
The pink-striped tyre is the softest in Pirelli's range and will make its race debut at the Monaco Grand Prix next week. We could just as easily go to the next race and struggle getting our tyres working and be nowhere.
Vettel will kick off proceedings in the Ferrari SF71H just two days after finishing fourth in Spain. There's been no weekends that I've been really way off the pace, like there was a few past year.
"I think it's pretty straightforward", he said. So I think I've learned from those.
GETTYSebastian Vettel on track during in-season testing
Ferrari was forced to end Kimi Raikkonen's race early with a suspected engine issue. "If we are not able to see that then we are more than blind", he said. No sooner would the race begin to settle than Esteban Ocon's Force India came to a halt, prompting the Virtual Safety Car.
Jack Aitken made his F1 debut in the Renault RS18 and completed 120 laps over the course of the day.
Hamilton is out of contract at the end of the season and his failure to put pen to paper on a new deal - worth a staggering £40m a year - had led to speculation he could walk away from the sport.
This week, we are looking at how the individual drivers in each team are performing.
"Obviously it looked like from the outside they [Mercedes] had a stronger weekend, without any big issues, but we need to look at ourselves, focus on our auto and our problems, so we'll be stronger again".
There was also more track time for Robert Kubica, who followed his FP1 run for Williams with a full day of testing and completed almost two race distances. Gasly was one place ahead of fellow F1 regular Vandoorne, who was driving a second McLaren dedicated to testing development tyres on a Pirelli-prescribed run plan. The Ferrari driver qualified and raced coolly ahead of the Red Bulls till he slowed mysteriously down and allowed those everrestless teammates to pass.