Speaking to RTE's Michael Corcoran O'Sullivan spoke of the pressure in the build up to the game
"It's pressure on and to be honest we wouldn't want it any other way. We said that we believed we could get further than the quarter-final. And we can. And that's pressure on ourselves to do what what's to be done to get there. It's a big performance against a very good team. It's the kind of pressure you want, the pressure and expectation that comes from playing well and winning games.
" Yes we know the French and how they play. They can tear teams to pieces. Certainly the conditions will be right for that. Not that we're complaining about that (conditions). We're happy about that. France are showing a consistency at the moment that would send out a warning. They're playing with a lot of width in their game. They're keeping their composure not missing their discipline. They're playing to a structure, but at the same time the flair's still there. They have a lot of pace, a lot of game-breakers. So it a fairly potent force.
"A lot of people are tipping them to win this World Cup now that they've timed their run so well after what was a bad summer for them. We'd like to think we'd have something to say about that.
"There will be doubts in the back of the French mind because they have lost three of the last four games against Ireland. Obviously bringing those doubts to the front of their minds is what we have to do Sunday.
"If we start well, get into them. When we have the ball, run at them, make them defend and when they have the ball, run at them knock 'em down. If we can do that then those doubts could creep into the front of the mind very quickly and it's a game for the taking then."
Nor is O'Sullivan too concerned with the programme that saw his side pitched into tough consecutive games against Argentina and Australia.
"No, apart from the injury count where we lost Denis Hickie and Alan Quinlan I 'm actually reasonably happy. It was a double-edged sword really. Being in a difficult group you mightn't get out and you're on your way home. But I always felt that if we got out of it we'd know our own worth.
"Again the fact we had eight days between games was colossal for us, absolutely huge. It's the difference between being battle-weary and battle-hardened. We're a very fit team at the moment but had we to play France six days after Australia I think now we'd be battle-weary. Now we're ready to go. Guys are in the zone now. They know what it's about. They're ready for the fight. I think we're in a good place."
"Things are coming together for us. Certainly to beat France on Sunday and be in the last four in the World Cup would be a milestone in Irish rugby. But it would also be a fantastic reward for a very good bunch of Irish players who worked very hard to get here and want to take the extra step."