Mortara had made a valiant charge through the field at Venturi's home race, rising from a lowly 16th-place grid slot to get well among the points.
This brought him onto the back of di Grassi and, with attack mode, Mortara made a move on the Brazilian driver to claim sixth place on the 24th lap.
But then di Grassi made contact with Mortara, handing the Swiss driver a puncture that eventually proved terminal as he limped to pits. Di Grassi hence reclaimed the position, where he eventually finished.
Recounting the incident, Mortara reckoned that di Grassi couldn't accept the idea of being passed by his teammate on track, and that a second consecutive race outside of the points was hard to swallow given his race pace in Monaco.
"[It went well] until I encountered Mr. di Grassi, my fellow teammate," Mortara reflected.
"I think the race was going on very well, from P16 to P6 with quite a lot of pace, and I was on attack mode and overtook Lucas.
"And I guess that he didn't accept it, his pride...I don't know, but anyway, he made contact with me and that caused us to retire the car because we had a puncture.
"It's hard, it's hard to swallow, especially when you have such a good race like this - it's difficult to overtake in Monaco and coming back from P16 to get into top six, top seven, it's always good."
Mortara felt that he was not out of the championship race just yet, remaining fifth in the drivers' standings but with a 22-point gap to Robin Frijns in fourth.
He said that, in addition to his race two retirement in Rome, he would have scored points in both and expected the championship to have looked different.
"In Rome I was sent off in the wall by Antonio [Felix da Costa]. And this one, I got also contact with Lucas.
"So that's two races in a row where we cannot score points. I think that we would have scored points in these two races. And in the championship, it would have looked completely different.
"We could have still been in the championship at the moment, like, there's a gap. It's not over but it's definitely really frustrating and we keep our heads up."
