Da Costa attempted to collect his second attack mode, a one-minute duration - on the 25th lap of the race - but missed one of the activation loops and was left without his second hit of 350kW power.
This had allowed Vergne to eradicate much of da Costa's advantage and ultimately collected the lead when da Costa took a more successful second pass through the Turn 12 loop.
Although this gave Vergne track position in the dying stages of the race, the nature of the fast and flowing Cape Town circuit meant that da Costa was able to pocket an energy advantage sitting in the Frenchman's slipstream.
This gave da Costa enough impetus to steal past with a stunning overtake on the outside of Turn 8, and held off Vergne over the final lap to claim victory.
"It was going very well. I did come back through the field, but actually I think Antonio's missing the technology is what made him win the race," said Vergne.
"Because then he pulled behind me and we had a huge amount of energy saving to do after the second safety car. And the slipstream is massive in that car.
"This is the moment where he could get more energy and put that attack on me. I think that if he didn't miss the attack mode, I would've stayed behind him, saved energy, and then maybe be in a position to make that move."
Vergne explained that he didn't see da Costa behind him prior to the Portuguese driver's move, and aimed his frustration at the mirrors on board the Formula E car.
Although not wishing to hide behind the mirrors as an excuse, countering that da Costa's move was "brilliant", Vergne says that being disappointed with second shows the progress DS Penske has made during the opening races.
"I'm just a bit frustrated cause I genuinely didn't see him coming," Vergne admitted.
"It's been like four or five races we complain about the mirrors; nothing has changed, nothing has been done. We simply cannot see anything in them.
"So I really hope they can come up with new mirrors very soon. In free practice, you impede a lot of drivers because you don't see them.
"I'm not going to use that as an excuse. He did a brilliant move, so let's be clear it's not an excuse.
"I'm a bit frustrated, but at the same time, I'm happy to be frustrated with second. We are coming back strongly in the championship that's the only thing that matters."
