But Wales' Leigh Halfpenny knocked over a last-gasp 30m penalty to deny the men in green the perfect start, afforded the opportunity when Wayne Barnes showed Ferris a yellow card for a tip tackle on Ian Evans.
However, O'Connell insists it would be too easy to use Ferris as a scapegoat, admitting the whole team need to hold their hands up in the defeat.
"I don't think it [Ferris tackle] was the winning and losing of the game," O'Connell told the Irish Times.
"I missed a tackle myself for their try late in the game and we probably gave them a lot of ball early on we shouldn't have.
"If you're going to leave it come down to one decision, pick out one player then you are not operating well as a team.
"There was disappointment. I think we put ourselves in a position to win the game and we conceded eight points in that five minutes and that's what cost us the game, not that one incident.
"I think we conceded a lot of momentum in the first half and gave them a lot of belief. We probably didn't defend with our heads up like we should.
"Our scramble defence was really good but we got caught on the short side once or twice. We gave them a lot of momentum and struggled to get into the game in that first half.
"It took us a while before we got a foothold on territory and play a bit of ball ourselves. When we did we scored a good try. You can't do that. You can't give a team that length of time with ball in hand. It puts you under a lot of pressure."