Peter Stringer is the big-name casualty to make way with the Munster veteran’s virtually uninterrupted reign as Ireland’s first choice number nine coming to an end.

The 29-year-old has paid the price for a dramatic slump that reached its nadir in Saturday’s 14-10 triumph over Georgia when he gifted the minnows an interception try that left Ireland fighting a desperate rearguard battle.

Support for Reddan’s promotion had been growing since the World Cup began and the weekend’s confirmation of Stringer’s deterioration in form made his claim impossible to ignore.

First-choice scrum-half for Heineken Champions Wasps, the 26-year-old has been highly rated in England and O’Sullivan has no fears pitching him into the biggest match of his career.

“It was a tough decision to make because Peter has been a stalwart of the team,” he said. “But his form lately hasn’t been the best – he hasn’t been on top of his game. He hasn’t been the Peter Stringer of old.

“Eoin comes straight into the side based on the type of game he’s capable of playing. His form for Wasps at the tail-end of last season was good and he fits the bill for this particular match.”

Stringer has been dropped just once before, against Scotland in 2001, and the ensuing defeat has been viewed as the beginning of the end for O’Sullivan’s predecessor Warren Gatland.

Axing such a prominent figure would have been a difficult move for O’Sullivan, but the under-fire Ireland boss insists he was left with little choice.

“It’s a tough call for a big game like this,” he said. “But like every player he accepts getting drops comes with the territory. It’s often the making of a player.

“I know he’ll bounce back from this. He’s been the heartbeat of the side many times before and he will be again. He knows better than anybody than anyone else that he hasn’t been on top of his game.”

There was not even room for Stringer on the bench with O’Sullivan opting to retain the versatility and game-breaking potential of Ulster’s Isaac Boss.

“We see Isaac as an impact player. He can also cover a number of positions and has performed to a high level,” he said.

In the two other changes to the starting line-up, one of which was enforced, Andrew Trimble replaces Denis Hickie on the left wing and Jerry Flannery profits from Rory Best’s dislocated thumb.

Trimble’s pace and power means he is preferred over Hickie, who is retiring from all rugby at the end of the World Cup, after a one-match spell on the sidelines with a fractured finger.

Flannery’s elevation to the side – long overdue in some eyes – see the fiery Munster front row make his first World Cup start.

“I wasn’t unhappy with Denis’ form but Andrew played well in the first game,” said O’Sullivan. “Jerry has been neck and neck with Rory for a last while. Rory has just held him out and is champing at the bit.”

In a puzzling final twist, Gavin Duffy supplants the versatile and talented Geordan Murphy as the wing/full-back cover on the bench.

O’Sullivan explained the logic behind the decision lay in Murphy’s last two displays against France, which saw errors by the Leicester back gift Les Bleus a total of three tries.

“Geordan’s last few games against France haven’t been a happy hunting ground. They have not been good days,” he said.

“That’s my decision and I stand over that. Gavin can cover wing, full-back and centre and that has also earned him the nod.”