Sainz, whose Toro Rosso team itself fielded an older-spec Ferrari engine last year, found himself stuck behind the Sauber of Pascal Wehrlein in the second half of the Spanish GP, after the German made his only stop of the race during the Virtual Safety Car period.

Sainz, running on medium tyres one lap fresher than Wehrlein's in the remaining laps, followed close behind the Sauber driver but couldn't find a way past - although he did move up one spot to seventh at the chequered flag, thanks to Wehrlein's pit entry penalty.

Despite having equalled his best finish of the season in what he described as an "intense" race, Sainz admitted he found the straightline speed deficit disconcerting.

"For the first time we were fighting the Sauber and it's a bit of a desperate situation to have a Ferrari 2016 engine faster than us on the straights, compared to our car at the moment," Sainz said.

"I tried my best to pass him, I was getting just enough to be side by side at Turn 1 but he was covering the inside line of Turn 1.

"It's tough to pass here but he was doing a good job to cover the inside line where he could - so good on him."

The data

On Saturday, Sainz and Wehrlein led their two respective teammates in the speed trap sheets in Barcelona, both clocking in at 318.4km/h,

But Sainz's teammate Daniil Kvyat and Sauber's other driver Marcus Ericsson were ahead in the race, at 334.7km/h and 334.1km/h respectively.

Kvyat, who fought with the Ferrari-engined Haas cars for much of the race and ended up ahead of both in ninth, said of the Renault power unit: "I don't feel it's the strongest engine, there's Mercedes and Ferrari, then there is somewhere Renault and maybe Honda.

"Today I was with Alonso and compared to me they were not that uncompetitive, they were strong on the straight actually. We are still behind, sure. "

Asked whether he agreed with Sainz's assessment that the Renault engine trailed the 2016 Ferrari, Kvyat said: "It looks like - ask Carlos. I was behind the 2017 Ferrari of Haas, it wasn't easy to pass but I had to pass in the corners."

Gain of three tenths will change "everything"

With reliability concerns having delayed the planned introduction of Renault's next engine upgrade, Sainz said he believes a gain of a few tenths on the power unit side will make a huge difference.

"We need a bit more power. You can see yesterday we were two tenths to P7, so imagine if Renault brings three tenths - suddenly everything changes.

"We need that step and it'll take probably another three races, so we need to be patient. We need to keep extracting what we have.

"In qualifying we are not where we want to be, but in the race it is better and better. It's been four consecutive races now where we try to fight back from a position in qualifying and I hope we don't do this all year. "

Additional reporting by Lawrence Barretto