While much of the focus around this weekend's meeting of Ireland and South Africa has centered on the physicality of the Springboks' seven replacement forwards, Bernard Jackman believes the breakdown threat of their subs could play an even greater role.

Ireland's scrum-halves have enjoyed lightning-quick service at the back of the ruck in their opening two games, with an average ruck speed of 2.91 seconds being the best in the tournament and the only team to average sub-three seconds.

In part, that ruck speed has been down to the standard of opposition, with Ireland having played their two weakest opponents in Romania and Tonga in the opening games. However, quick ruck ball has been a constant theme of Ireland's play across their record 15 wins in a row.

Ireland have been among the best in the world on both sides of the ball at the breakdown in the last two seasons, with the likes of Peter O'Mahony, Josh van der Flier and Tadhg Beirne noted for their ability to win turnover ball at the ruck.

That breakdown control will be heavily tested against the world champions, who many feel have the largest and most physical pack in the game.

In addition, head coach Jacques Nienaber has loaded his bench up with extra forwards, opting for a 7:1 split in comparison to Ireland's 5:3. Barring injury, it means only one of the Springbok pack will have to play the full 80 minutes.

And while many observers been fixated on how Ireland will cope with the size and power of the South African subs, Jackman believes their own noted breakdown specialists will pose a greater threat to Ireland in the game's defining moments.

"We think of the 'Bomb Squad' as seven forwards coming on and a power game up front," he told the RTÉ Rugby World Cup podcast.

"I actually think the challenge for us is the last 20 minutes and being able to keep the ball at the breakdown, because it's ridiculous the threat they’re bring in, if you have [Marco] Van Staden, Deon Fourie, Kwagga Smith on the field at the same time when you’re tired, when the game traditionally has become easier to win the ball.

"The last quarter, statistically is Ireland’s best by a long way, so at the time we’re hoping to increase the tempo or to find holes, if every single breakdown is a car crash and slow, then we’re screwed.

"The 'Bomb Squad’ this week is basically the ‘Breakdown Squad’."

Jackman was joined on the podcast by South African native and former Scotland attack coach AB Zondagh, who is currently based with French Top14 side Lyon.

And Zondagh believes Ireland's ability or inability to create quick ruck ball will be the winning and losing of the game.

"I think the big turning point will be what happens at the breakdown," he said.

"If you look at the 7:1 split, Ireland could be facing a total of five or six fetchers on the field at one time, so there's no hiding that strategy either.

"South Africa is going into that game to absolutely disrupt that attack, to turn that ball over. And that’s probably bigger than the kicking game, bigger than the physical game, that’s where the game is going to be won and lost, first and foremost.

"If that ball is slow, South Africa has a much better chance of getting to Sexton, getting up into that space and cutting off their options. For me, that’s the key."

It was on their run to the 2019 Rugby World Cup title that South Africa's replacements earned their nickname, the 'Bomb Squad', with the likes of Malcolm Marx, RG Snyman and Franco Mostert allowing Rassie Erasmus's side to physically dominate their opponents for 80 minutes.

With dominant set-pieces, their attack was relatively simple and based around kicking and squeezing opponents into errors.

In the last 18 months there has been a real pivot in their attacking game under Nienaber, and while they have evolved their strategy, Jackman says they haven't lost any of their physical edge.

"They know what they want," he added.

"It sounds cheesy listening to Chase the Sun [South Africa’s 2019 World Cup documentary] or whatever, but any of the inserts we get into the mentality [of the Springboks], it’s: 'F*** them up’. That’s what they say behind the scenes, and that’s great. It’s part of the South African rugby DNA, it doesn’t mean they can’t be skillful or creative, it’s who they are.

"I think they have evolved and they’ll certainly hurt you if you don’t defend properly, but I don’t think it’s going to be the biggest test of the day.

"I think we can stop them up front, if we get blown away there it won’t be like the England World Cup final where the scrum was the Achilles heel. But can we take away the energy from their game by hurting them with the ball? That doesn’t have to be running it, it can be kicking it. We have to do that, or it becomes suffocation and it’s horrible.

"Ireland have been building for this, it’s four years worth of work to have the skillset to maybe execute two passes in a millisecond. That’s the margins."

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Watch live coverage of Ireland v South Africa (Saturday, 8pm) on RTÉ2 and RTÉ Player, listen to live commentary on RTÉ Radio 1, and follow live updates on RTÉ Sport Online and the RTÉ News app.