The Irish have claimed one victory from their two tournament matches with an unconvincing win against Italy and a remarkable 43-31 defeat by France.

Wales provide the next assignment and O'Sullivan believes success at Lansdowne Road has the potential to nudge Ireland onto the path of RBS 6 Nations glory.

Next weekend would have been a pivotal game in the Six Nations regardless of whether we had won or lost in Paris, he said.

It is the middle game and entering it with two wins as opposed to just one can define your Six Nations, no matter whether you are England, France or Scotland.

If we get a result on Sunday we go into the Scotland game with everything wide open for us.

It is similar to two years ago when we lost in Paris, our second game was against Wales and then our middle game was against England.

We beat England and that turned our championship in the right direction.

Wales have been hit by the loss of Gareth Thomas to a damaged neck artery and O'Sullivan, who worked with the Toulouse full-back on last summer's British & Irish Lions tour, believes his absence will be keenly felt.

Gareth is a world class player and is a loss to them. We have lost Paul O'Connell to injury so I believe that's a fair trade off in the circumstances, he said.

It's a very unusual injury he has got. Gareth has been an ever present in the Welsh team for almost 10 years now. He has become a talisman for them.

He was superb on the Lions tour - he is a great captain and a very charismatic guy. I wish him well. The sooner he gets back the better for Welsh rugby. He has been hugely influential for them.