Irish star O'Mahony wins 100th cap for World Cup decider with Scots

Peter O'Mahony will become the latest Irish player to reach a landmark 100 caps for his country on Saturday when Ireland face Scotland in a match pivotal to both sides' Rugby World Cup hopes.

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The 34-year-old flanker was named on Thursday in a side showing just two changes to the starting XV that impressed in the 13-8 win over defending champions South Africa a fortnight ago.

Head coach Andy Farrell has brought in hooker Dan Sheehan in preference to Ronan Kelleher whose line-out throwing was awry in the first half of the Springboks match.

Ireland captain Johnny Sexton blamed Kelleher's poor throwing more on bad calls and this may account for Iain Henderson coming into the second row with the line-out caller James Ryan dropping to the bench.

There has been talk of Ryan having a hand injury.

However, his demotion is still a surprise as the Leinster star has been an ever present in the starting XV under Joe Schmidt and then Farrell with him deputising for Sexton as captain when the latter has been unavailable.

O'Mahony becomes the 10th player to reach the milestone for Ireland, following in the footsteps of current team-mates Sexton, Conor Murray and Keith Earls.

He made his debut for Ireland in a 42-10 win against Italy in February 2012.

Ireland will start as hot favourites to book their ticket in the quarter-finals -- probably against New Zealand -- with a record-extending 17th successive Test victory.

The Scots have it all to do to end a run of eight consecutive defeats at the hands of their opponents despite two morale-boosting wins over Tonga and Romania.

Ireland

15 Hugo Keenan; 14 Mack Hansen, 13 Garry Ringrose, 12 Bundee Aki, 11 James Lowe; 10 Johnny