Strategy behind Perez and Force India's Russian GP podium 'on edge'

The Mexican scored the third podium of the team's Force India era as he finished third behind Lewis Hamilton's Mercedes and Ferrari's Sebastian Vettel at Sochi.

When Lotus's Romain Grosjean hit the barrier to bring out the safety car on lap 12, fifth-placed Perez was one of only four drivers to dive into the pits to swap his super-softs for the soft tyres.

That left him with 41 laps to complete on the same set of tyres, but he held third with two laps to go and then regained it when Valtteri Bottas and Kimi Raikkonen collided after overtaking him.

When asked if Perez was comfortably in the window to make the crucial stop without needing a further tyre change, Fernley said: "It was very on edge.

"Nobody in front of us followed suit, so it gave us the advantage.

"The core was to look at it from the point of view that it could be an exceptional result or if it went wrong it would probably be a good result.

"Hopefully we can carry it through to a good result in Austin and Mexico."

Fernley added he was "reasonably" confident the tyres would last, adding: "It was a long safety car so that helped, but it was marginal.

"Pitwall and driver, together they did a great job.

"That was teamwork, they are trying to guide him as best as possible within the limitations and Sergio as always delivered a fantastic result."

Perez's haul of 15 points meant Force India increased its lead over Lotus to 26 points in the battle for fifth in the constructors' championship.

"It has put some clear air between us and we need it because Lotus is a good team," said Fernley.

"It only takes a good weekend for them and we're under pressure again."