Kimi Antonelli lowered the benchmark for this week’s Formula 1 pre-season test at Barcelona on Thursday while the new Aston Martin hasn't made its on-track debut yet.
With the pace and reliability of the new W17 having impressed rivals, Antonelli set a new quickest time of the week with a 1m17.081s as he continued to rack up the miles.
His best time beat the previous fastest lap of the week, set by Antonelli himself on Wednesday, by three tenths of a second.
It also means Mercedes has gone faster this week than its best race lap from last year's Spanish Grand Prix - highlighting that the 2026 cars appear to be in a similar laptime ballpark to the previous generation of cars.
Mercedes has done little this week to weaken its status as the pre-season favourites, with both its pace and reliability strong.
Antonelli's closest challenger on Thursday morning was Oscar Piastri, who was getting his first taste of the new MCL40 after team-mate Lando Norris gave it a debut outing on Wednesday.
Piastri set a best lap of 1m18.419s and completed 48 laps.
Lewis Hamilton in the Ferrari was third quickest, having suffered a small spin early in the morning coming out of Turn 10, when out on cold tyres.
His best lap in the end was 1m18.654s, although direct comparisons are hard to make as teams can be running very different programmes.
Liam Lawson in the Racing Bulls was fourth fastest on a 1m18.840s with Sergio Perez in the Cadillac the only other runner on a 1m21.349s.
Aston Martin's new 2026 car is expected to run later on Thursday, with the team not managing to make it out in the morning session.
Unofficial times, Thursday morning
1 Kimi Antonelli (Mercedes) 1m17.081s (90 laps)
2 Oscar Piastri (McLaren) 1m18.419s (48 laps)
3 Lewis Hamilton (Ferrari) 1m18.654s (87 laps)
4 Liam Lawson (Racing Bulls) 1m18.840 (64 laps)
5 Sergio Perez (Cadillac) 1m21.349 (38 laps)
