Renault's Nico Hulkenberg was having a fairly quiet pre-season test – at least until the German came out of nowhere on the final day of the first week to post the fastest time seen so far in Barcelona this year: a 1m 17.393s.
With whispers up and down the pit lane of the top teams sandbagging, Hulkenberg headed an unusual classification at the end of Day 4 - at least according to last year's form guide - with the Toro Rosso of Alexander Albon in second and Hulkenberg’s Renault team mate Daniel Ricciardo in third.
It wasn’t all positive for the German, however, as he ended his afternoon in the pits having stopped out on track with an undiagnosed issue on his R.S.19. In fact, despite their timesheet-topping antics, Renault recorded fewer laps on the final day than on any other.
Behind the top three, the two Mercedes drivers finally gave us a little flash of the pace that many believe is lurking in their W10 – despite Valtteri Bottas’ words to the media in the Day 4 lunch hour including that his new car’s balance was “on a knife-edge”. They went fourth and fifth, Bottas ahead of Hamilton.
Ferrari rival Charles Leclerc – who was fastest on Day 2 – ended the day sixth, although his fastest time was set on the medium C3 Pirelli tyres, while Hamilton was on the C4s and the top four were on the softest C5s.
Testing Day 4: Late Hulkenberg stoppage brings out the reds
Having been hampered by reliability issues throughout the test, Haas enjoyed a smooth run through Day 4 to clock over 200 laps between Kevin Magnussen (returning to the cockpit after the team resolved the headrest issues that side-lined the Dane on Tuesday) and Romain Grosjean.
The day was less smooth, however, for Antonio Giovinazzi, who brought out the red flags twice in the last 10 minutes of the session when his Alfa Romeo C38 stopped out on track. By that point, however, the Italian had clocked 154 laps - eight more than Red Bull's Pierre Gasly, who did the next most on another day in which Red Bull were low-key but quietly confident about progress with their Honda power unit.
Having arrived late in Barcelona, Williams were trying to make up for lost time, with both Robert Kubica and George Russell spending part of their running with a large aero rake set up strapped to their cars, as the team try to unlock the secrets of their FW42. It was a slightly scrappy return to front-line action for Kubica, meanwhile, as the Pole suffered two spins, whilst also blocking both Lewis Hamilton and Charles Leclerc at various times throughout the first session of the day.
So chapeau to Renault for finishing the first week in Barcelona on top – but expect more to come from the likes of Red Bull, Ferrari and Mercedes when Week 2 gets underway on February 26.