Mercedes has revealed how close Valtteri Bottas was to not making it to the end of Sunday's Spanish Grand Prix.

Having made his sole stop of the race on lap 19, six laps before his teammate, Valtteri Bottas faced the daunting task of making his medium tyres last another 47 laps.

In its latest Pure Pitwall presentation, the German team's chief strategist, James Vowles, reveals just how marginal it was for the Finn in the final stages of the race.

"It's fair to say that it was extremely marginal," says the Briton. "It's fair to say that if the race had been a lap or two longer, we could have been in big, big trouble.

"The last few laps of the race for Valtteri were very, very tense," he continues. "We knew that the front left tyre would be very much down to zero rubber remaining. And it's a very difficult call as to what's going to happen. But he had eight seconds of race time relative to the Red Bull behind, and what we were trying to do was very delicately use up some of that race time to slow down in some of the key corner sequences to make sure we looked after that tyre whilst not losing temperature in the rubber that was still actually left on it.

"It's a very, very delicate balance," he admits, "and I really can't understate this, Valtteri did an absolutely incredible job. We put him in a very difficult position, and he dealt with it absolutely perfectly, taking that tyre just to the end of the race as we asked him to do."

The Briton also revealed the thinking behind the strategy was the firm beleif that Red Bull would be running a one-stop strategy.

"What we concluded based on all the evidence that we had is there was as strong possibility of Vettel taking it, and it's extremely unlikely that anything else would have happened if we took it, rather than just staying behind Vettel, and Red Bull, and therefore finishing lower than the P2 that was the potential in the car.

"We decided to take the risk, we took the tyres to the end of the race. It was extremely close, it was a very tight judgement call, but it ended up on the right side for us on that occasion."