Is Mercedes fighting Ferrari or itself?

Ferrari's decision to fast track its Spec-2 engine for this weekend's Spanish Grand Prix, two races before it had been originally scheduled, shows the significance of its need to achieve a good result immediately.

While Ferrari's car has shown promise in the opening four grands prix of the season, its failure to turn that potential into wins has left it on the back foot against a stronger-than-ever Mercedes - which has nailed a record-breaking four straight one-two finishes to start its campaign in perfect fashion.

Ferrari knows that the gaps in both the constructors' and drivers' championships cannot get much bigger if it is to have a realistic chance of turning things around in the title chase: and the only way to ensure it remains master of its own destiny is to go out there and produce a flawless weekend.

While it's a situation that leaves a tremendous amount of pressure on the shoulders of Ferrari's team boss Mattia Binotto, it would be wrong to say that his opposite number at Mercedes Toto Wolff can head to Spain in a relaxed mood either.

The reality is that the Barcelona weekend will be equally as defining for Wolff too, because it will lay out the issues he will face over the remainder of the campaign.

Even having won the first four races, and coming off the back of five straight F1 world titles, the stresses for Mercedes' top brass have not got any less. It's one of the downsides of top-line sport: it is just as difficult being at the front and staying there as it is playing catch-up.

Yet another Ferrari failure would effectively kill off realistic hopes of a fightback

For Wolff, the 2019 season is now likely to head in one of two trajectories, neither of which are going to be easy. But then again, he has never shown himself to be someone to shy away from challenges.

One path is a full-blown title fight with Ferrari. At a track where the red cars showed so well in winter testing, and motivated by an engine that should give it more of an advantage in an area where it has already been strong, a Ferrari victory at last would signal that Mercedes' fear about the strength of its rival was fully justified.

But there is another direction that could open up this weekend. Yet another Ferrari failure to win - on a weekend when it has thrown it all in with its Spec-2 engine - would effectively kill off realistic hopes of a fightback. It would not be over by any stretch of the imagination (and it's never finished until the maths say so), but the chances of recovery would be slim.

The fading of the Ferrari challenge would instead open up the prospect of a different kind of battle for the 2019 title: a straight head-to-head between Lewis Hamilton and Valtteri Bottas.

Bottas 2.0 has caught the attention this year, and the perception of him - both internally and externally - is of a changed man. Sharp eyed viewers of Mercedes' regular YouTube Pure Pitwall video debriefs spotted a big bag of porridge on the desk behind strategy chief James Vowles as he reflected on Baku: a clear reference to the new breakfast of choice for the Finn...

So far relations between Hamilton and Bottas have been without hitch: and there has been a marked contrast between how things are now and the tensions that sometimes overshadowed things when Nico Rosberg was there.

Hamilton himself said several times last year that this is the best relationship he has had with a team-mate. But those comments came at a time when Bottas was going through a down period and didn't look like posing a regular threat.

But could the new Bottas - who has deliberately adopted a more steely edge to his approach - threaten the harmony within the team if his run of recent success turns into a full-blown title assault?

Would Hamilton be forced to respond to a team-mate who has the chance of overhauling him for the title? Would Hamilton so readily give Bottas the space at the first corner like he did in Baku, an action he later suggested he slightly regretted?

After the Azerbaijan GP, Nico Rosberg - who managed to beat Hamilton to the 2016 world title before his shock decision to retire - suggested that Bottas did have what was needed to pull off the championship.

"Valtteri really has a chance this year to be champion because it is a different Valtteri we are seeing, and everything is going his way as well," said Rosberg on his YouTube channel.

"Last year he had a lot of bad luck, now he has had a start of the season where everything is going his way so it just gives you a completely different mindset and puts you in a different confidence level as well, and that just matters so much in sport.

"So Valtteri now has really high confidence and he can continue fighting Lewis the next couple of races. He does have the chance to win the championship, there is no reason why not.

"We want them to be lions in the car, so you can't expect the behaviour of a sheep" Toto Wolff

"He is driving strongly, in all qualifyings he is right there with Lewis's pace so he is really doing well.

"It is amazing how it can go from one season to the next: last year Valtteri was in no man's lands and suddenly over the winter, probably learned some things from me as well in how to reset over the winter and come back strong. And not focus on Lewis, but focusing on yourself and getting the job done.

"That is what matters and Valtteri is doing that, so hats off."

Rosberg's comments about lessons from him could, perhaps, include the factor that he succeeded in getting underneath Hamilton's skin.

During the height of their rivalry, there was little love lost between them - and Wolff will need no reminding of the stress he faced in 2016 when he had to deal with collisions between the pair in Spain and Austria.

For now Hamilton is sanguine about the situation, and reckons it impossible to predict how things could develop.

"I can't tell you what will happen further in the year, I can't judge if one's character will change or not," he said of the potential for a different relationship with Bottas. "Drivers in the past didn't stick to rules of engagement that we have as a team. And Valtteri and I do, or Valtteri does."

For Wolff, more success for his team in the next few weeks - and potentially a killer blow against Ferrari in Spain - would provide just brief relief: for the focus would then be on dealing with an internal title challenge that can be just as fraught.

Already in Baku, Wolff was aware of the potential for a repeat of the Rosberg/Hamilton rivalry as another one-two was rolled out.

"I think we are lucky that they have a very good relationship," he said. "They get on with each other. There is not a lot of games in the background, and I'm very happy about that.

"But as a matter of fact we have to be conscious that we have seen relationships deteriorate.

"Both of the drivers have an ambition to win the championship. We want them to be feisty in the car, lions in the car, so you can't expect the behaviour of a sheep.

"But the respect needs to stay in there and we're very strong as a team and we wouldn't allow a relationship between drivers to deteriorate to a point where it has a negative effect on the team.

"If that would ever be the case again, we will issue yellow and red cards. But we are not there."

Indeed, so far all is well. But come Sunday night in Spain, we will have a much better idea of what storms may be on the horizon - and whether they are blowing in from Maranello or could be forming much closer to home.