Ireland head coach Declan Kidney says the desire 'to find out more' about young flyhalf Jonathan Sexton was the ultimate deciding factor which saw him selected ahead of Ronan O'Gara for this weekend's clash with the Springboks.

Kidney, selecting his side to take on the World Champions at Croke Park on Saturday, handed Sexton his international debut against Fiji last weekend but now, up against South Africa, Kidney believes his young star will be able to show what he is really capable of.

Not since 2003, when David Humphreys faced Argentina at the World Cup, has a different flyhalf started for Ireland against a major Test nation.

O'Gara has started every single Six Nations match for the past six years - a run of 30 games - and has only been rested when on duty for the British and Irish Lions or against minor opposition.

But his form during the past two years has been inconsistent and, now 32, will be 34 by the time of the next World Cup, in New Zealand in 2011.

Kidney knows that, at the very least, Ireland need a credible deputy and, after announcing his team to face the Springboks, he told reporters on Tuesday: "I know we have a world-class outside half in Ronan but we have to find out things about ourselves.

"Jonathan had a good game last week but with respect, Fiji were short of a few so it was difficult to read. I need to find out more.

"I worked with Jonathan last year and gave him the nod for the 'A' team and that answered a lot of questions."

Answering questions about what the effect of the landmark call might have on O'Gara, Kidney said the Munster star has taken the setback in his stride and insists that he remains very much a part of the Ireland team.

"I know we still have Ronan available. He's disappointed he's not playing but I can't pick everybody all of the time.

"Ronan is disappointed but is the perfect pro. He's taken it on the chin, has continued training and has contributed to the team exactly as he would normally.

"It was a difficult call but that doesn't really matter. My job is to pick the Ireland team and that's what I've done."