Jarvis, Josh Pierson and Giedo van der Garde beat team-mates Phil Hanson, Freddie Lubin and Ben Hanley by 0.68s in Portugal on Sunday, despite Jarvis needing to rely on pitboard communication from his team during his closing double stint.
Van der Garde had been due to see out the race with a triple stint, but was brought in for Jarvis after only one of them when the team lost communication with the #23 ORECA-Gibson 07.
However, what the team believed to be a problem with van der Garde’s helmet proved to be related instead to the car, so Jarvis faced a tricky ask to combine chasing the leading Prema ORECA of Daniil Kvyat with working out fuel permutations and when he needed to make his final pitstop.
“It wasn’t an easy race,” explained Jarvis, who had lost a likely win last time out in Sebring due to a freak problem as the in-car camera was shaken loose by the circuit’s famous bumps and knocked the kill switch.
“I was done and got the call 30 seconds before Giedo boxed to get ready, jumped in and unfortunately there was an issue with the radio on the car side.
“I kind of had to think for myself and we managed to make it work.”
The arrival of the safety car when Jacques Villeneuve suffered a brake failure in his Vanwall Hypercar compromised Prema’s tyre strategy, wiping out Kvyat’s advantage and leaving him with a choice between losing track position to change tyres or trying to extend their life.
After racing resumed, Jarvis remained close enough to jump Kvyat as he ran one lap longer, which he admitted had been a risk.
Speaking to Autosport, Jarvis revealed it was “the first time I’ve finished the race without a radio”.
“It’s not easy with the safety car procedures and then you’re trying to work out the fuel save,” he said.
“I must admit they were giving me fuel numbers on the pit board and I’m thinking to myself, ‘they were quite aggressive’ and I couldn’t fully understand why.
“We still had fuel at the end of the first stints, but we boxed early to cover everyone else in case there was a safety car and all the time I’m trying to calculate all of this in my head.
“They told me to box and I wanted to stay out. I wanted to push one lap and try and jump the Prema.
“I realised what they wanted to do was box as soon as they could fill it and go to the end, and you do that in case there’s a safety car because otherwise you can go from first to last.
“But at the same time, every lap you stay out is a risk. So I knew by staying out my neck was on the line, but I wanted the win.”
As Kvyat faded to fourth at the end, Jarvis was then faced with pressure from team-mate Hanson but managed to keep him at bay.
The reigning IMSA SportsCar champion added that he was unsure when the checkered flag would be coming out.
“At the end they’d given me a fuel consumption and it was trying to manage that but also I wanted to make sure we kept the lead,” Jarvis told Autosport.
“Sometimes I was a bit over it, sometimes a bit under it, but it worked out in the end.
“I didn’t know when the checkered was coming, so I was a bit relieved that it came out when it did.”
