Instead, it's their attitude off track and, more importantly, the passing of what could be called a 'crash test', that has left their chief convinced the pair have massively bright futures in F1.

Passion is key

The fight to make an impression at Red Bull's junior F1 team has always left its drivers facing a high pressure situation.

But this year, both Verstappen and Sainz have embraced the opportunity – and a decent chassis – to impress onlookers.

There have been races where the pair have qualified high up the grid, strong race performances and in Hungary, Verstappen took a career best fourth-place to show how much progress he has made.

And although it is Verstappen who has grabbed the headlines thanks to his age, and that big Monaco accident and fallout, Sainz has shone with some very strong performances as well.

Passion and intelligence

For Tost, the performance of both is something to be proud of, although he is taken aback by just how good they are in their approach to the job.

"I must say, both of them really are doing a fantastic job," Tost told Motorsport.com. "Why are they doing a fantastic job? Because they are committed to F1.

"I think both of them have a real positive attitude. F1 is their life, which means also between the races, they are all the time in contact with the engineers, they do concentrated physical training, they go to the simulator, and they are well prepared.

"They are always on time, they ask many questions and I am really quite positive about their way of working.

"You do not need to tell them – you have to do this or do that. They do it already. That is decisive.

"It is their inner wish to be successful. It is their passion, and their passion is one of the most important factors to be successful. They both have the passion."

The crash test

But it is not just in attitude and results that has left Tost raving about his line-up, for he also takes heart from the fact the pair have hit trouble too.

Tost is a great believer that all drivers go through a similar schooling in F1 – and to pass their initiation there need to be some accidents along to way so they know where the limits are.

"It is the usual story when young drivers come into F1," he explained. "The first three/four races they will never crash – because they have the respect to come into F1.

"They always think: 'I must be careful, and I must be cautious. I must not risk much, I must make kilometres and I must make the chequered flag'.

"But the drivers are already nearly on the limit from the physics of the car because of their good education in the younger classes.

"We have now by far the best generation of young drivers I have ever worked with. It is unbelievable how well educated they are coming into F1.

"So, after three or four races, they think F1 is easy. And they think, 'now I will show the people how fast I am really'. And then, what I call 'the crash period' starts.

"This crash period is necessary because it helps the drivers understand the limit of the physics and therefore these crashes are important.

"You can tell to the driver beforehand, 'don't do this or don't do that'. But it is useless. He has to experience it himself.

"F1 is very complicated, like not to be too close in braking areas because you lose front grip with dirty air etc., but he has to learn this.

"For this he has to spin or be in the gravel, or crash. And that is okay. That is always what I calculate and this is always what I say in advance

"And this is the case with these drivers. We saw crashes and spins from both drivers: and that is normal and the price you have to pay if you have young drivers in the team.

"We have two young drivers and it depends how skilled they are to shorten the crash period and see how fast they are learning."

Best Toro Rosso line-up

Tost has no doubt Verstappen and Sainz have come through that crash period well.

And, having seen some bright talent through the Toro Rosso ranks over his time – including Sebastian Vettel, Daniel Ricciardo and Daniil Kvyat – he is well qualified to talk about just how good his current men are.

In Sainz and Verstappen, he is convinced at this stage the pair have delivered more than any other line-up – and that means they have the potential to be the overall best.

"I think at the end it is the most competitive driver pairing up until now," he said. "Now, we must see.

"For me it is always very important how is the gradient of the learning curve. And for me up until now it has been very, very steep.

"If it continues like this, then it is for sure by far the best driver combination we have had."