Ireland were 13-3 down within 14 minutes of Sunday's RBS 6 Nations clash with France and it was not until the second half that they finally overhauled the deficit.

A last-gasp try from Vincent Clerc saw France snatch victory in a shattering blow for the Irish given the heroics performed in pegging the champions backs.

Sluggish starts have defined many of Ireland's games in recent times - their 47-second try in this season's opener against Wales was an exception - and O'Sullivan knows this shortcoming must be addressed.

'We need to improve the way we open games. We need to stop getting on the back foot early on, absorbing pressure and then fighting to get back into the match,' said the head coach.

'We must set our marker down early defensively, not sitting back waiting to see what they do. We need to knock people over and once we do that our game ticks over pretty well.

'We give up positions to easily in the first 10-15 minutes and then start the engines up. I'd rather we started the engines up at kick-off.

'I don't know why we start slowly. Sometimes it's because it's easier to play with the ball and get into the game, making the opposition defend.

'But if you don't have the ball then you have to get off your line defensively and sometimes we're hesitant doing that early in the game.'

Ireland's chance of toppling France were hit by the loss of Brian O'Driscoll to a hamstring strain but the talisman skipper will be back to face England on Saturday week.

O'Sullivan has sufficient playing resources to paper over the cracks when O'Driscoll is absent but he admits in reality the dynamic Leinster midfielder is irreplaceable.

'We're missing the best international centre in the world, and that's no reflection on Shane Horgan,' he said.

'No-one would argue with the fact Brian O'Driscoll was a loss against France.

'I don't want to go down that road too much because it's not fair on the lads who were on the pitch, but he's a loss and there's no doubt about it.

'I don't think any country in the world could replace Brian O'Driscoll if they had to. It did hurt us not having him and it was tough leaving him out.

'I knew that no matter how well we prepared, there wouldn't be that edge to our attack and defence without him.

'I said at the outset of the Six Nations that injuries would have a bearing on the championship. It's unfortunate but that's the way it is.

'There's no point saying we don't miss him.'