For too long O'Sullivan has not trusted the quality of his bench, preferring to stick by his starting XV when the opposition launched fresh units at key strategic moments.

In the two Six Nations games against Italy and France however, O'Sullivan, in response to the World Cup disaster last year, has introduced more players from the replacements while there has still been enough time to make an impact.

Most notable was the change in Ireland's fortunes during the final quarter in the narrow defeat to France recently as the visitors increasingly gained an upper hand.

And a quick glance at Ireland's reserves today suggests that if O'Sullivan continues such a policy, Scotland will not be able to cope with the introduction of such heavyweight players.

O'Sullivan can call on such experienced campaigners as Paul O'Connell, Rory Best, Simon Easterby and Shane Horgan while in contrast, Scotland's bench looks sparse with only Chris Cusiter and Dan Parks looking capable of a major impact.

Ireland too will look to hold more than their own up front, buoyed by their scrummaging performance against the French.

So much of Scotland's game is based around a quick ball produced by midfield targets or pick-and-drives by their big forward unit and if Ireland can slow that down, the home defence should be able to cope with what ever is thrown at them.

"Physically Scotland have been very hard for us to handle in the past couple of years and we lost a lot of collisions," said O'Sullivan.

"Last year at Murrayfield in the Six Nations it was a hugely physical game and they disrupted us by being in our faces. It took us a long time to wear them down.

"It was more of the same in August when we also didn't cope very well with the physicality Scotland have used to great effect over the past couple of years.

"It will be physical again tomorrow and we have to make sure that we break even - at the very least - in that area of the game."

It will be interesting to see if O'Sullivan's counterpart Frank Hadden produces any surprises today.

Certainly the selection of Chris Paterson at out-half suggests Scotland will attack the wide channels more often.

The Scottish coach, after two defeats, knows the pressure is mounting following a wooden spoon finish last season.

With O'Sullivan also under huge pressure to, the match could well prove decisive in both men's coaching international coaching careers.

With so much at stake, O'Sullivan however still had words of support for his counterpart.

"The pressure is part of the job," added O'Sullivan. "Frank has done one hell of a job with Scotland over the last few years.

"He's been very successful at coming in, taking a style of playing and deciding to change it in the belief the players he has are capable of doing certain things.

"Scotland have been a very different team to play against under Frank. In sport if you win by a point everything is right, if you lose by a point everything is wrong.

"I have huge respect for him and the Scotland team since he's taken over.

"We've found them very difficult to play against, and that's the job any coach wants to do. I wish him well, but not until Sunday."

IRELAND: G Murphy (Leicester); T Bowe (Ulster), B O'Driscoll (Leinster, captain), A Trimble (Ulster), R Kearney (Leinster); R O'Gara (Munster), E Reddan (Wasps); M Horan (Munster), B Jackman (Leinster), J Hayes (Munster), D O'Callaghan (Munster), M O'Driscoll (Munster), D Leamy (Munster), D Wallace (Munster), J Heaslip (Leinster). Replacements: R Best (Ulster), T Buckley (Munster), P O'Connell (Munster), S Easterby (Llanelli), P Stringer (Munster), P Wallace (Ulster), S Horgan (Leinster).

SCOTLAND: Southwell (Edinburgh); Walker (Ospreys), Webster (Edinburgh), Henderson (Glasgow), R Lamont (Sale); Paterson (Gloucester), Blair (Edinburgh, capt); Jacobsen (Edinburgh), Ford (Edinburgh), E Murray (Northampton), Hines (Perpignan), MacLeod (Scarlets), Strokosch (Gloucester), Hogg (Edinburgh), Brown (Glasgow). Replacements: F Thomson (Glasgow), Kerr (Edinburgh), Hamilton (Leicester), Rennie (Edinburgh), Cusiter (Perpignan), Parks (Glasgow), De Luca (Edinburgh).

Referee: Christophe Berdos (FRA).