Time was when a victory of any manner would have been a good enough reason for leaving well enough alone, never mind one by 69 points. But in making four changes for the visit of the Springboks this Sunday, the Irish management have acknowledged that - no disrespect to the relatively diminutive Japanese - here come the big boys.

Aside from the change at full back, where Geordan Murphy's demotion to the A team already signalled the return of Girvan Dempsey, Rob Henderson has been preferred to Shane Horgan at inside centre, Gary Longwell will make his first start in place of Paddy Johns, and Eric Miller comes into the back row instead of Andy Ward at blindside flanker.

It may be some consolation to the deposed quartet that the management also repeated, like a mantra, that the changes were all close calls.

The demotion of the Ravenhill cult hero Ward will certainly have disappointed many in Ulster after his productive ball-carrying and hard-working display against Japan. But against that, the return of the multi-faceted Eric Miller, after an impressive run of form with Leinster, is a welcome opportunity for a rare talent that has yet to fulfil its immense promise. It may be Miller's 20th cap, but he has won five of his last six from the bench, and, with all due respect to the USA Eagles last summer, this is Miller's most meaningful international since he started the defeat in Murrayfield two seasons ago.

Explaining this selection, Warren Gatland said: "He's trained particularly well in the last couple of weeks. In terms of the selection there were a number of very tight calls and we just felt that there was absolutely nothing in it, but that Eric was the right decision for this game against South Africa.

"This is taking nothing away from Andy against Japan. We were happy with his performance. It was just a very tight call, but we felt that Eric has come into a bit of form for the last few matches for Leinster and he may be the player to do a job on this occasion."

Perhaps too, on some subliminal level, the sight of the Springboks may act as a catalyst for Miller to rediscover some of the brilliance he showed in midweek games for the Lions against the same opposition three long summers ago. Now almost four years older and wiser, Miller has also played all his rugby this season on the blindside, whereas Ward is a converted openside. And, as Gatland revealed, Miller's abilities at the tail of the lineout was a factor.

The rationale for preferring the tried and trusted Henderson over Horgan was akin to that which applied at full back. Although Eddie O'Sullivan acknowledged that it was a tough call on Horgan in demoting him to the bench, bearing in mind his five tries in five Tests on the wing last season, it would have been harsher to drop one of the wings to move Horgan back there.

"Again, a very difficult decision," said the assistant/backs coach. "Despite the fact that the midfield did very well on Saturday and it's a combination we looked at, maybe they just need a little bit more to go before they really click. We know what Rob brings to the table and we just felt that, for this game in particular, a one-off against South Africa, it was the right decision to put him in there. But again, not much in it, a tight call. Just a gut feeling on it for this one."

While the return of the more experienced and established Dempsey and Henderson may confirm the impression that last week's selection had been experimental, clearly the change in the engine room is more a reflection on how Longwell and Johns are motoring of late, and how last Saturday reaffirmed that impression.

Longwell has been an ever-present for Ulster in their 10 games to date, whereas Johns, battling injuries, has started only six games for his province; last Saturday was his first start in four weeks, and he was replaced by Longwell after 56 minutes.

It doesn't say much for the progress of the young second rows around, especially World Cup squad member of a year ago Bob Casey. A couple of seasons ago Longwell would have been a long way off, and his fitness levels would not have been of the requisite standard. But, buoyed by Ulster's European Cup run and the advent of professionalism, his vast improvement in this regard was amply evident, for example, in his huge tackle count and the number of rucks he hit against Cardiff in the European Cup win at home.

Though he is more, by nature, a middle of the line jumper and will have to adapt to operating from the front on Sunday, Longwell is thus seen as overtaking Johns.

"Again a very tight call," said Gatland. "When we selected the squad originally Gary was in our discussions from the start. We're very impressed this year in the way he played for Ulster. His work-rate's been excellent, he's a big man and he just got the nod. To be honest, some selections were very tight calls and it was sometimes just a gut feeling on players hopefully doing a job for us on the day."

For all the upheavals South Africa have experienced this year in a rollercoaster season, Gatland pointed out that their squad includes 24 from the recent Currie Cup final. "They've been playing at the top level, they're coming off the end of their season, they'll be physical and fit and in good shape, so I think there's undoubtedly real quality in their side. It's a huge test for us."

The Springboks arrived late yesterday afternoon, and may announce their team tomorrow. It's likely to fall along the lines of the side which beat Argentina 37-33 last Sunday, and is drawn from a full-strength squad save for the injured trio of scrumhalf Werner Swanepoel, the brilliant back row Rassie Erasmus and prop Cobus Visagie, who not only has a broken wrist but also needs to clear his name after a positive drugs test.