Ireland's lineout was below par on the night, with five throws out of 20 lost and the Triple Crown winners never built a possessional platform out of touch.
Speaking straight after the 25-3 defeat, O'Sullivan said: "Obviously we're disappointed to be beaten. The better team won. There were areas where I was disappointed. Number one was our discipline which up to half-time was eight against us. That's as many as we gave away in 80 minutes of a rugby game last season.
"France built a lead based on our indiscipline. If we'd gotten to half-time at just 9-3 down, I would have taken that as a pretty good return on our investment in the first half but we gave away another penalty right on half-time.
"And after getting ourselves good field position at the start of the second half, a lost lineout and two penalties later we were 15-3 down and that was really the cushion that France needed.
"We had an uphill climb after that and to compound matters our lineout didn't fire tonight. We were looking to win a lot of lineout ball tonight so that we could attack France but we never secured the quality ball we needed. As a result, we never got on the front foot. So, a combination of a lack of discipline and a poor lineout put us in a very bad place," he admitted.
Ireland's lack of control at the breakdown and other areas was punished unflinchingly by referee Chris White, and O'Sullivan felt that the English official was too excessive with his penalties against the men in green.
"We had problems with the referee who I thought blew us off the park. Chris is good ref, we've had him many times before, but I thought he penalised us excessively. At the same time our discipline is usually excellent but tonight it killed us. We have to live with what happened now."
Whilst disappointed about the result, the Corkman reckons the nine day gap between this match and their next against Argentina at the Parc des Princes will give him and his coaching staff ample time to prepare for what has to be a big win over the Pumas.
"It's the Pool of Death and we always knew there was a chance it could come down to the last game. I'm happy we've a nine day turnaround and it gives us time to get a plan in place for playing Argentina," he added.
"We've a couple of days off now so we'll take a look at what went wrong tonight and put a fix on it and then start trying to get the players right for Argentina. Obviously, we've to try to work out what went wrong but at some stage you have to look ahead to the next challenge and that's Argentina."