Troubled Ireland received a welcome boost with the news that Gordon D'Arcy, Rob Kearney and Sean O'Brien should be fit to line up against United States in their rugby World Cup opener.

Ireland have endured a woeful warmup campaign, losing four matches against Six Nations rivals in August and having first-choice openside flanker David Wallace ruled out of the tournament last week after suffering a long-term knee injury.

Centre D'Arcy (calf), fullback Kearney (groin) and flanker O'Brien (knee) were also fitness concerns for the September 11 clash in New Plymouth but the trio should all play with only prop Cian Healy (eye) likely to miss the match.

"We know that Cian and Gordon are coming out, I think they fly out tomorrow Dublin time and the latest information is that they are on track," Ireland's Australian defense coach Les Kiss told reporters in Queenstown on Saturday.

"Rob trained part of the session yesterday but he will be in full training this coming week as will Sean O'Brien, so everything seems to be pulling in the right direction.

"Cian is the only one that may have a little bit of doubt over him at this stage."

The news is a welcome boost to a side whose expectations of topping Pool C, which also features Australia, Italy and Russia, have diminished heavily after their string of defeats and the Wallabies' Tri-Nations title success last week.

"We didn't get the results we wanted in the warm-up games but in terms of the planning we were absolutely spot on," Ireland's South African forwards coach Gert Smal told reporters.

Smal was part of the Springboks World Cup success four years ago and says Ireland, who are seeded to meet South Africa in the quarter-finals, have enjoyed a good preparation despite the losses.

"I would say, better than what we (South Africa) had in 2007, in the amount of detail we put into planning with everybody, the whole pre-season, organising game time for the players and getting to the stage where we are at the moment.

"I have tried to share as much as possible of my 2007 World Cup experience with (head coach) Declan (Kidney) and the management.

"What I did right back at the beginning when I joined Ireland (in 2008), I organised for Declan to sit down with (South Africa's 2007 World Cup winning coach) Jake (White).

"I organised a meeting between the two of them to share their experiences and, with that kind of background, the whole preparation (has been) spot on - we just have to start producing now."

A familiar face that Ireland will have to contend with in their opening match will be their former coach Eddie O'Sullivan, who is now in charge of the U.S. Eagles.

O'Sullivan, who was dismissed in 2008 after Ireland's dismal World Cup campaign where they exited in the group stages after almost losing to lowly Georgia, did not expect much from the clash with his former team.

"We're realistic, we've got three tier one nations in our pool and obviously Russia is the big game for us," O'Sullivan said.

The match falls on the 10th anniversary of the attack on the twin towers in New York and O'Sullivan said he would have to work on containing his player's emotion for their benefit.

"Motivation isn't going to be an issue for these lads, they're always easy to fire up. It's going to be emotional I think.

"For me, part of my job is to contain the emotion. If they get too emotional, they'll make mistakes, and if they make mistakes they'll pay a big price."

Reuters