Mercedes' decision to not pit Valtteri Bottas for a second time during the Spanish GP was extremely marginal and could have severely cost them, they revealed yesterday.
The Constructors' Championship leaders opted to change Bottas' tyres on lap 19, six before teammate and eventual race winner Lewis Hamilton, but meant that the Finnish driver had to complete 47 laps on his medium tyres before reaching the chequered flag.
Mercedes could have brought Bottas in for a quick tyre change at the same time as Sebastian Vettel, with the German pitting under a late virtual safety car, but the F1 team decided against a second pit-stop as they pushed to gain track positions.
Chief strategist for Mercedes James Vowles said that had they chosen to bring Bottas in, he would have been stuck behind Red Bull racers Max Verstappen and Daniel Ricciardo, who were running a one-stop race.
"It's fair to say that it was extremely marginal, that if the race had been a lap or two longer, we could have been in big, big trouble," said Vowles.
"Valtteri did a very good job, especially managing that front left tyre, that was the weak tyre, the tyre that had to be looked after quite a bit whilst still maintaining performance.
"We were never going to bring Valtteri in in the last few laps because we had the confidence that it was just going to make it.
"At the end of the race it was all about using up some of that race time that he had accumulated relative to Verstappen just to make sure that we absolutely made it to the end of the race."
While it was at his own team's risk, Vowles admitted Bottas did an "incredible job" of extending his tyres' life in order to ensure he completed the race.
"The last few laps of the race for Valtteri were very, very tense," said Vowles.
"We knew that the front left tyre would be very much down to zero rubber remaining.
"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 to slow down in some of the key corner sequences to make sure we looked after that tyre while not losing temperature in the rubber that was still actually left on it.
"It's a very, very delicate balance, 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."
Mercedes will look to take their winning form from Spain across to the next GP in Monaco on May 27.