"It's important to get off to a good start in the World Cup and we are going with experience to boost our chances." the Irish coach said today after announcing his side for the opening game.
O'Sullivan believes that, "the team that wins the World Cup is the team that copes with pressure the best. The pressure starts now and goes on until you get on the plane to go home.
"There is a sense of relief now that the team has been announced. There is a good buzz in the camp. Guys are on their toes. We hit the ground running when we arrived in Australia and we have been surprised at the intensity that we brought with us. But the guys who have been selected are under pressure. They are the lucky ones to get in but they must now deliver a performance.
"We've picked a strong side, but if we had picked a much different one it would have been equally as strong. That's the strength in depth we have in this squad.
O'Sullivan forewarns that Ireland is in for a tough fight of it against the Romanians."They are physical. They have a grizzly pack. They are good ball carriers. They have a strong scrum and a good line out. We are the favourites to beat Romania, no two ways about that - but being favourites brings its own pressure.
"If it takes 79 minutes to win, I can cope with that. Teams are going to throw the kitchen sink at you and you have to expect that on Saturday with Romania.
"You can get carried away thinking about scoring four tries to win a bonus point. It is more important to win than to try and score X and Y. The purpose is to win and after that if you can get the bonus point, all very well and, of course, we would hope we can do that.
"The key for Ireland is to focus on our goals - the things we can do to control the game, that's the nuts and bolts.
"Winning your line out, winning your scrums, getting over the gain line, running good lines of attack and then when they have the ball making your tackles, building your defence. We know if we deliver our goals, we win the game - and that's pressure."
Nor is he too concerned about bring Shane Horgan straight back into the side after a long absence, "Shane's been flying in training, He's had good rehab and it's not a problem bringing a winger back like this. It's different for a forward and that's why we've put John (Hayes) on the bench. We could have given Shane a run for Leinster before we left. But why run the risk. He's here now. He's fit and raring to go."
Ireland. 15-Girvan Dempsey (Leinster-Terenure College)14-Shane Horgan (Leinster-Lansdowne)13-Brian O'Driscoll (Leinster-Blackrock College)12-Kevin Maggs (Bath)11-Denis Hickie (Leinster-St. Mary's College)10-David Humphreys (Ulster-Dungannon)9-Peter Stringer (Munster-Shannon)1-Marcus Horan (Munster-Shannon)2-Keith Wood (Munster-Garryowen) capt 3-Reggie Corrigan (Leinster-Greystones)4-Malcom O'Kelly (Leinster-St. Mary's College)