The Mercedes Formula 1 team has admitted its decision not to pit Valtteri Bottas for a second time in the Spanish Grand Prix was "extremely marginal".
Bottas stopped for medium tyres on lap 19, six laps before team-mate and race winner Lewis Hamilton, and had to complete 47 laps on them before the chequered flag.
Mercedes opted not to bring Bottas in for new tyres when Sebastian Vettel pitted under a late virtual safety car, preferring to jump the Ferrari and gain track position while Vettel dropped behind Max Verstappen.
Chief strategist James Vowles said Mercedes had put Bottas in a difficult position, but knew that had he stopped for fresh tyres he would have rejoined behind the Red Bulls of Verstappen and Daniel Ricciardo that "were absolutely going to make that one-stop work".
Although Mercedes was confident that it had got its sums right, Vowles admitted it was a close call.
"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 in a Mercedes video.
"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."
Vowles stressed Bottas did an "incredible job" of managing his tyres and extending their life so he could reach the flag safely.
"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."