The Brazilian had taken Julius Baer Pole Position but found himself on the defensive from the two-thirds point of the race having fallen from the lead into third, with the Porsche-powered Avalanche Andretti of Jake Dennis and factory Porsche driver Pascal Wehrlein romping by earlier in the encounter.
He was a percent or so down on usable energy compared to those immediately around him and it took all of his guile and experience to see off the attentions of NEOM McLaren's Jake Hughes over the closing stages.
Eventually, though, the rookie would be preoccupied with Andre Lotterer (TAG Heuer Porsche) looming in his mirrors, relieiving the pressure on di Grassi; who felt that he and the team delivered the absolute maximum from the package currently beneath them.
“What happened today was like a Mexican miracle," said the 2016/17 champion. "To be on pole and to be on the podium and going home with 18 points after a tough beginning to the season is a testimony to the hard work the team are putting in to make the car the best we can.
"I gave it my all today to try and make the team proud. I’m very happy to leave here with this result, it feels like a victory to us. But this is just the beginning. We need more consistent results and we have got to work hard for this.”
"It was a very, very tough race. Of course, we are not in this race for the win, we knew that the Porsches would be extremely fast - remember last year that they won one and two, and they disappeared, so it was impossible to hold.
"I was running low on energy, but I tried to defend as much as I could. In the end, the podium is like a win to us. We did only three or four days with this car - there is still so much potential to take it out. I'm super happy."