That's the dilemma currently facing ACT Brumbies coach Stephen Larkham as he weighs up who to start at flyhalf in Saturday's sudden-death semi-final against the Waikato Chiefs.

In one corner is Noah Lolesio. The 23-year-old with 17 Wallabies caps to his name and the man who steered the Brumbies with aplomb all season.

But Lolesio suffered a concussion in the round 14 loss to the Chiefs, opening the door for Jack Debreczeni to step into the No.10 jumper.

The 30-year-old has been superb throughout the past two weeks, guiding the Brumbies past the Rebels before producing one of the best halves of footy you'll see in Saturday's quarter-final win over the Hurricanes.

Lolesio made his return off the bench on Saturday, injected into the contest in the 68^th minute with the game in the balance.

The playmaker didn't let his team down, playing a role in Tom Wright's go-ahead try before nailing a conversion from the sideline that effectively won the match.

So what is the Brumbies coaching staff to do?

"What a challenge, hey," assistant coach Rod Seib said. "They're two fantastic players who have been doing great things. Jack with a man-of-the-match performance, he controlled things very well, his kicking game was on song, he was sort of pulling the right cord at the right time in terms of decision making.

"Then you have Noah come on off the bench and kick one from the sideline, which was one of the key ingredients for the win.

"They say it's a good challenge for the coaches to have those sort of discussions but it certainly doesn't make it any easier."

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Seib and Larkham have had extensive conversations over what to do with the No.10 jumper, with a decision expected to be made on Tuesday morning.

While one man will start and one will be injected off the bench, Seib expects both players to play a key role in Saturday's semi-final against the Chiefs in Hamilton.

The Brumbies have turned to their reserves to deliver at the death on a weekly basis, the likes of Blake Schoupp and Luke Reimer producing match-defining plays.

It was Reimer who got his arm underneath Ardie Savea as the Hurricanes captain dove towards the line on Saturday night, sealing a famous quarter-final victory.

The art of making an instant impact is not an easy one, but Seib said the coaching staff work hard to equip their players with the necessary skills to do so.

"For me it's really just around job clarity, isn't it?" he said. "They've got to understand what their point of difference is and what they need to bring to the game in the last 20 minutes.

"Luke Reimer for example, he knows his point of difference is that poach threat. So he's got to be making sure he's in a position to deliver that.

"Regardless of what position they are, they all know very clearly what they've got to add when they come on and they can't just join in seamlessly. They've got to actually make a difference and they all know how they can do that."

The Brumbies preparations for Saturday's semi-final have been given a major boost with New Zealand-born duo Tamati Tua and Ollie Sapsford re-signing with the club for the 2024 season.

The pair have shared the No.12 jumper throughout the year, combining with Len Ikitau in the centres.

Sapsford, however, shifted to the wing on Saturday night in place of speedster Corey Toole and did not skip a beat.

Toole is in a race against the clock to overcome an ankle injury and will be given every opportunity to prove his fitness.

"We'd love to have [Toole] available," Seib said. "At 75 per cent he's still quicker than most blokes. It would be great to have him there but we'll see from the medicos if he's available or not."

Sapsford's path to the Brumbies was an eventful one, featuring stints playing AFL in Perth, rugby sevens for New Zealand and for Hawkes Bay in the NPC but he's found a home in Canberra.

His versatility in the backline has proven crucial this year and he's determined to deliver on Saturday and throughout 2024.

"It's awesome to have next season sorted and to be staying here in Canberra with the Brumbies," Sapsford said.

"I'm grateful to the club and the coaches for taking a punt bringing me over and for working with me, and to the boys for welcoming me in. Playing more this year, I've felt even more a part of this club and I'm excited to be going home this week as a Brumby and with this team."

Tua followed his fellow Kiwi across the ditch and has emerged as one of the hidden gems of this year's competition.

The former Auckland Blue has provided a unique option in the centres and his combination with Ikitau has improved each week.

Tua conceded it was a tough decision to move to Australia but said it has helped him become a better player.

"Leaving home last year, getting out of comfort zone was a big change for me but I'm happy I made the decision to come to the Brumbies," Tua said.

"The boys have been great, and I'm enjoying the lifestyle here in Canberra so I'm excited to stay."

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