Though he topped the timesheets at the Yas Marina today, Sebastian Vettel's efforts were comprised by an early off that resulted in him damaging the rear wing on the Ferrari, and couple of subsequent punishing rides over the notorious kerbs which damaged the car's floor.
"The purpose of this test is primarily to get a first feeling of the new tyres, with the impressions of the last weekend of racing still fresh in our minds, which gave us the possibility to compare," he said.
"Unfortunately, today we lost some track time to repair work, but overall I think there were no major surprises as these tyres seem to work and to be fairly similar to the ones we used this season.
Now we'll see how the new regulations for 2019 affect the speed of all cars and how they work in combination with the tyres, also depending on the compound choices at the various tracks."
Asked how the 2019 compounds compared their 2018 counterparts, he said: "The differences were quite small. Speaking to Pirelli, the whole band is a little closer together so the hypersoft is closer to the rest and the hard tyre, which we didn't use, should be more towards the tyres that are softer."
Tomorrow, for the second and final day of tyre testing, Charles Leclerc will take over with a similar programme.
At Mercedes, Valtteri Bottas completed 120 untroubled laps at the wheel of the championship winning W09. The Finn his fastest time on the hypersofts.
"Overall, a good day," he said. "We completed our programme without any issues and we were able to do some long and short runs on a mix of the new Pirelli compounds.
"We can see some differences to this year's tyres," he continued, "but we have all winter to work on understanding the new tyres from all the knowledge we are gaining from this test. I'm sure Pirelli will learn a lot from these two days of testing as well. We'll be back on track tomorrow for the final time this year.
"Today was about gathering data on the 2019 tyres and understanding how they differ to the 2018 tyres we've used this year," added Andrew Shovlin. "We'll continue our programme with Valtteri tomorrow with more of a focus on the performance and degradation of each of the compounds.
"This work is important as we need to select tyres for the early races based on the information we find at this test. It was a good day of running and the car ran without any issues."
One of the main media attractions today was the Force India garage, where Lance Stroll was making his debut. Sergio Perez drove in the morning, completing 67 laps and posting a best time of 1:37.976 on the softest of the 2019 tyres available.
Taking over in the afternoon, Stroll completed a further 56 laps for the Silverstone-based outfit, posting his best time (1:37.909) - which just happened to be the third best time of the day - on the hypersofts.
Max Verstappen was on duty for Red Bull, the youngster completing 131 laps on his way to the fourth best time of the day.
One of a number of teams to feature an all-new driver line-up next season, McLaren got its preparation underway with Lando Norris, who will be partnered with Carlos Sainz next year.
As the test is dedicated to tyre testing, car development is naturally limited. However, there is much still to be learned ahead of the 2019 season, not only tyre degradation, but also useful driver-specific procedures and processes.
"I think this was the most laps I've ever done in a day, so it was good," said Norris, who completed 135 laps, the second most of the twelve drivers on duty. "I got through a lot of the things I needed to, such as longer runs – which I haven't done much of so far – so considering all that, I don't feel too bad. I haven't really felt the degradation of the tyres before, so that was one of the biggest things I wanted to get through.
"I'll have a bit more experience for next year now, of tyre drop-off and things like that," he added. "I also wanted to put a few other things together, such as practice starts and giving feedback.
"It did feel a bit different today, realising that a lot of the stuff we did was for my own good and things that will really benefit me a lot next year. I'm now trying to get everything based around me rather than the other drivers like in the past as Test Driver, so it definitely did feel a bit different. I really wanted to focus on trying to make it the best I could for me, so it was useful."
"For us, today was the first day of our 2019 programme successfully completed," said Sporting Director, Gil de Ferran. "We had a clean day and accomplished all of our objectives, including several longer runs. Our focus was not only collecting tyre information, but for the first time the programme was geared towards Lando as our main priority, rather than the supporting role he has played as test and reserve Driver so far. We're looking forward to having Carlos drive our car for the first time tomorrow."
Days after his spectacular barrel-roll, Nico Hulkenberg was back in action for Renault. The German, showing no after-effects from his big crash, completed 128 laps.
Haas began its programme with Pietro Fittipaldi making his Formula One debut. The youngster completed 56 laps of the 3.451-mile, 21-turn track. His quickest time was a 1:39.201, set on his 41st lap on a set of hypersoft tyres. It placed him eighth of the twelve drivers on duty.
Fittipaldi wasted little time getting onto the track when it opened, making his installation lap on ultrasoft tyre. A 17-lap run on the same compound followed. The morning program then stopped abruptly due to an electrical power unit issue as he began his next out-lap shortly before 11:00.
After an extended stay in the garage for a power unit change, he returned to the track just after 16:00. He quickly cycled through back-to-back comparison runs utilizing Pirelli's 2018 and 2019 soft and hypersoft rubber. He totalled 38 laps to close a productive final two hours of track time.
"It was an amazing day," beamed Fittipaldi. "I'm very happy to have had my first drive in a Formula One car. The braking power of the car, the acceleration, the speeds you carry through the corners, it was just insane. The car is so fast. It's just stuck to the ground. The amount of downforce it has is unbelievable.
"We had small issues at the beginning of the day, but the team got them sorted. They really did a fantastic job to get back out there, and then in the afternoon we worked through the plan we had. We compared the 2018 tires to the 2019s from Pirelli. I tried to give the engineers my best feedback so they can start working on that information.
"The team has given me a huge opportunity to be testing with them next year. I'll learn as much as I can, but also help them with developing the car for 2019 and throughout the season. It was a really good test."
Like Force India, Williams had two drivers on duty, with Robert Kubica and George Russell completing 74 laps between them and separated by just 0.243s.
At Sauber, Kimi Raikkonen made his much-anticipated return to the team with which he made his F1 debut in 2001. The Finn completed a total of 102 laps throughout the day, becoming familiar with the car and the team's operating systems.
The programme was focused on tyre testing - running the 2019 tyre casing - as well as different compounds from the current selection.
With the Finn feedback and the collected data, the team obtained a good reference in preparation for the upcoming season.
Unfortunately, on the final run, the Finn stopped out on track meaning the session had to be red-flagged, though according to Sauber the stoppage did not compromise the programme. As a result of the stoppage, the cause of which is not yet known, the session was extended by a further 15 minutes.
Though Alexander Albon was confirmed as Toro Rosso's second driver yesterday, for contractual reasons Sean Gelael was on duty today.
The youngster completed 150 laps - the most by any driver - on his way to posting the twelfth best time of the day.
Check out our Tuesday test gallery from the Yas Marina, here.