Jared Payne loss tips balance further in Springboks' favour
To lose one of your starting centres from this year's Six Nations was a problem, to lose two is potentially disastrous for Ireland's prospects of winning a Test series in South Africa.
Confirmation that Jared Payne will sit out the Port Elizabeth decider as a result of a calf injury he suffered during last week's defeat at Ellis Park means that Joe Schmidt goes into the final Test just three of his starting backs from this season's Six Nations.
Although he, like most others, faded in Johannesburg, Payne has been an assured presence in the backline all season and his display in the opening Test in Cape Town suggested he was in for a long run in the No 15 jersey.
That changed this week when Robbie Henshaw returned home and Schmidt must have been tempted to redeploy Payne into his midfield.
Instead, the inexperienced trio of Tiernan O'Halloran, Stuart Olding and Luke Marshall will occupy the Nos 15, 12 and 13 jerseys, having never played together at this level before.
While this tour was always about getting experience into new bodies, it is hard to envisage Schmidt ever planning on going into a decider with that combination outside the callow Paddy Jackson.
Yet he expressed full confidence in his side's ability to do themselves and their country justice at the Nelson Mandela Bay Stadium.
"I'm utterly confident that they'll make me and themselves proud," he said.
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"They'll make sure that Ireland feels proud of them because that's the way they commit to going about their work and I've no doubt that they'll be no different than it has been in the last two Tests.
"Yes, it's been a long season, people are tired and that's going to maybe detract from people being at their optimum, but I don't think too many people will detect that because what they don't have in fresh reserves of energy, they'll make up for in the full commitment they make to doing the job that they do."
While the backline may have been weakened by the enforced changes, up front Schmidt has re-introduced the players who did so well in Newlands and were rested for the second Test.
Mike Ross returns, with Tadhg Furlong back on the bench to provide impact, while CJ Stander's return from suspension sees Iain Henderson return to the second-row.
Stander will be joined by Jordi Murphy on the flank as Rhys Ruddock is back among the replacements.
There also looks to be more fire-power for Schmidt to bring on, with Sean Cronin and Ultan Dillane named on the bench, along with Matt Healy, who can win his first cap.
For their part, the Springboks have made two predictable changes as Waren Whiteley and Ruan Combrinck come into the side after coming off the bench at half-time last week and making a huge contribution.
Allister Coetzee has resisted any urge to make further changes, but Jaco Kriel - a star of Super Rugby in recent seasons - comes on to the bench.
"They both scored tries and they both made a real impression away from scoring those two tries as well so that's not that surprising," Schmidt said.
"I guess Allister's just started with this group and to build rhythm; I think you need a little bit of continuity and to get cohesion, if you are chopping and changing a lot it does make that quite difficult.
"They certainly appear to be a fairly fresh bunch, therefore there's no real need to be resting anybody so it's not too much of a surprise with the way they finished last week that those two players have come in and the rest of them have been retained."