A series of fine saves from Pompey goalkeeper Trevor Carson had kept Wycombe at bay before the ball was cleared off the Bury loanee's line several times in one goalmouth scramble after the break.
And Ainsworth insists Fodgen's reaction after the penalty incident was telling as the midfielder appeared not to make any signs of protest to referee Charles Breakspear.
"It was the softest penalty you have ever seen, I don't think any Portsmouth players appealed for the penalty, but he just seemed to give it," said Ainsworth, whose side are winless in 2014.
"I disagree with the decision, but I can't question anything else, he's the referee and he can only see what he sees on the pitch.
"That was their only shot on goal and they scored it. The difference is they put their chance in the back of the net, and in fact we did as well, again I question that decision.
"I thought the ball went into the back of the net, on the goal-line, but if it looks out, it's out."
- Sports & Recreation