Ireland and Wales have both made changes in key positions for this weekend's Six Nations Championship title showdown here at the Millennium Stadium.
Victory for Ireland in Cardiff on Saturday would see them win only their second Grand Slam in history to set alongside their 1948 triumph.
Wales, whose hopes of back-to-back Slams disappeared with a 21-16 loss to France in Paris last month, must win by at least 13 points if they are to deny the Irish a first Championship since 1985 and retain their title.
Ireland coach Declan Kidney had reacted to his side's 22-15 win away to Scotland last time out by recalling scrum-half Tomas O'Leary in place of veteran Peter Stringer and bringing back both No 8 Jamie Heaslip and hooker Jerry Flannery.
Kidney, typically, was reluctant to explain why he had made his changes after unveiling the team on Tuesday. "It's not horses for courses. That can be a bracket. Our aim is to be as good as we can be on any given day."
Wales coach Warren Gatland, the former Ireland boss, was heavily criticised for making nine alterations to the team that was narrowly beaten by France ahead of last week's stuttering 20-15 defeat of Italy in Rome.
The former Ireland boss has responded by announcing eight changes on Tuesday and all but reverting to the side beaten by France.
Star flanker Martyn Williams, lock Ian Gough and prop Gethin Jenkins all return to a pack that was overpowered in the scrum at the Stadio Flaminio while in the backs centre Tom Shanklin starts alongside 2005 and 2008 Grand Slam midfield colleague Gavin Henson.
Ryan Jones, Wales's Grand Slam-winning skipper last season, regains the captaincy from Alun-Wyn Jones.
Shanklin, who scored Wales's winning try in Rome eight minutes from time after coming on as a replacement, starts in place of Jamie Roberts while Stephen Jones is restored at outside-half instead of James Hook.
"I don't mind admitting we have left ourselves with a lot to do to win the Championship," said Gatland.
"But, on the other hand, the 13-point deficit is by no means insurmountable," the New Zealander added.
Teams for the Six Nations international between Wales and Ireland at the Millennium Stadium here on Saturday (1730GMT kick-off):
Lee Byrne; Mark Jones, Tom Shanklin, Gavin Henson, Shane Williams; Stephen Jones, Mike Phillips; Andy Powell, Martyn Williams, Ryan Jones (capt); Alun-Wyn Jones, Ian Gough; Adam Jones, Matthew Rees, Gethin Jenkins
Robert Kearney; Tommy Bowe, Brian O'Driscoll (capt), Gordon D'Arcy, Luke Fitzgerald; Ronan O'Gara, Tomas O'Leary; Jamie Heaslip, David Wallace, Stephen Ferris; Paul O'Connell, Donncha O'Callaghan; John Hayes, Jerry Flannery, Marcus Horan
Referee: Wayne Barnes (ENG)
Source: AFP European Edition