Sebastian Vettel and Valtteri Bottas were the clear pace-setters at Barcelona as pre-season testing got underway.

Let's be crystal clear, this is not only pre-season testing, it is the first day of pre-season testing, indeed, it is the first morning of pre-season testing. Therefore, take it all with a pinch of salt, particularly in terms of pace.

That said, while Ferrari and Mercedes are the early pace-sestters, 2017 preparations got off to the worst possible start for McLaren.

Having completed just one lap, Fernando Alonso – sporting a helmet the bore a zebra design similar to the test livery that adorned the Red Bulls a couple of years back - was sidelined by an "oil system issue".

A bad enough problem at the best of times, but let's not forget that this is pre-season testing and the teams have just eight days in which to prepare for Melbourne. This is not the sort of issue that McLaren (or Honda) can afford at this time.

Nico Hulkenberg had the honour of being first out, followed by Magnussen, Massa, Ericsson and Bottas, all as eager to get back to work as the fans are to see them.

While Red Bull insists on doing all it can to prove that triskaidekaphobia - fear of the number 13 - is a load of baloney, the team appeared to have incurred the wrath of the gods when Daniel Ricciardo caused the first red flag of the year.

As the team posted a gif on Twitter depicting a black cat strolling through its Milton Keynes HQ, it was revealed that the RB13 had suffered a sensor issue, which, as it requires the removal of the gearbox, is bad news for the Austrian team.

The only other incidents of note were when Magnussen stopped at the pit entrance and later spun at T10 damaging the front wing of the Sauber as he clouted the barriers.

While Vettel tops the timesheets, it is Mercedes which has really impressed, Bottas completing a couple of long runs – totalling more than a race distance in the process - and for much of the morning setting the pace.

"It already feels like another category compared to last year; so much downforce!" enthused Carlos Sainz, and while nipping at the heels of the Williams, it is noticeable that the Force India - on initial evidence - is best of the rest.

As fans continue to lament the awful fins that are so prominent this year - Mercedes rumoured to be trying theirs on Wednesday - a number of teams have been running T-wings on top of the fin - or 'sails if you prefer.

All this morning's running has been on mediums, only Bottas and Perez venturing on to the softs.

All in all, a pretty uneventful morning, and while we wait to see it Red Bull is going to be mixing it with the Mercedes and Ferrari, the main interest is whether McLaren-Honda can get its act together this afternoon.

With Mercedes continuing the same strategy seen during the 2016 tests, Lewis Hamilton takes over from Bottas for this afternoon's shift.

Check out our Monday gallery from Barcelona, here.