The Franco-Argentine was running ninth on the final lap, trailing the Maserati MSG car of Mortara, but was struggling to mount a challenge owing to the flat-out nature of the race's last throes following a safety car period.
Having noticed Mortara trying to save energy ahead by lifting early, Fenestraz decided to make a move on the Swiss driver and try to double his points haul in one fell swoop.
Admitting he was "a long way back" and was risking everything to potentially finish the race "on three wheels", Fenestraz launched an assault and came up for air with eighth place in his grasp, getting Nissan off the mark for 2022-23.
"It was so fun!" the former Super Formula driver told Autosport when asked to explain his move on Mortara.
"Basically after the safety car, it was nearly a flat-out race for everybody, so there was absolutely zero chance of overtaking, unless you take a big, big risk, which is very tricky.
"You can see from even Sam [Bird], some so experienced - he tried and he went straight off. So it is very tricky to overtake in this car, and even more when it's an end of the race like this.
"We were all kind of a flat out race, but I could see Edo was lifting a little bit in some points.
"I was like, for sure he has still to save some energy. And on the last lap I saw he lifted and I was like... man, I was quite far back.
"And I was like, let's give it a go to the finish line. He's just there, I can finish in three wheels, it's okay!
"I just went in and I passed. There was a bit of contact, but it's Formula E..."
Fenestraz added that claiming his first points was a sign of improvement from Nissan after a low-key start to the season, and that its strategy with attack mode had been well-executed.
He explained that the team still had work to do to improve its fortunes, particularly as Nissan has not been able to consistently match its partner McLaren team.
"I was really happy with that move and it was a great race. I feel like I managed the race, the strategy of the attacks early in the race were good," said Fenestraz.
"Overall, I think we executed everything pretty well. We still want to work a lot as we are still not where we want to be, but it was a big improvement from the team side and on my side, just score my first ever points in this very difficult track.
"Honestly it's crazy, the level of this [championship]. I'm very happy for the team, but we are here to win - the team is here to win, I'm here to win.
"We've got to keep on working hard, but of course, the result is good and cheers up the team after a difficult Mexico, and a difficult [Friday race]."
