Former Ireland head coach Eddie O'Sullivan says Saturday's Test with world champions South Africa is the "real deal".

The sides will also meet in Pool B in the World Cup in France next year.

"There is no doubt we are the best team in the world, but I have a feeling the Boks are going to come and try to upset the applecart," said O'Sullivan.

O'Sullivan told BBC Radio Ulster's Sportsound Extra Time that Ireland have a "nice balance" in their three autumn internationals with Fiji and Australia to come after Saturday's opening Test at the Aviva Stadium.

Ireland claimed a historic series win over New Zealand this summer which lifted them to the top of the rankings.

"It is a good autumn series for Ireland and they will have a pretty good gauge of where they are," O'Sullivan said.

"We have found in recent years that when the Boks have come, they have not been at the calibre or the pitch you would expect from them.

"We have got them and beat them. But I think this Boks team, who have come with Rassie Erasmus, will want to make a statement.

"If the Boks show up in full force then it will be a great Test. If we can beat them, albeit in Dublin, it will copper fasten our position in world rugby.

"We deserve that position at the moment. The result in New Zealand was fantastic, but we did see how New Zealand are probably not where they want to be."

'South Africa will throw down a marker'

O'Sullivan, Ireland head coach from 2001 to 2008, said South Africa will want to take the "bragging rights" before the World Cup meeting.

"It is going to be a really good Test, it will set out exactly where we are," he said.

"If we can win that game, if it is a big barn burner of a game and we come out on top, there will be no argument about it.

"I don't think Australia are where South Africa are or even where New Zealand are. The Springboks are coming to throw down a marker.

"This will all be decided over two hours next Saturday. If Ireland are going to establish themselves as the bona fide number one, this is a game they will want to win to double down on that.

"If South Africa were to turn them over then the bragging rights might change position again."