The Triple Crown winners dispatched South Africa 32-15 last Saturday but are braced for a more challenging test of their growing stock in Test rugby against the Wallabies.

With two dazzling backlines and similar sized packs, O’Sullivan claims the sides are so evenly matched the outcome will be decided by his coaching duel with opposite number John Connolly.

“We’ve lost our last four games on the bounce against Australia so the omens aren’t good for beating them.

“Against Australia you don’t know what is going to happen. It’s a very tactical game and I enjoy that in the sense that there’s a lot of coaching to be done on the day.

“You have to adjust the game-plan around what’s happening in front of you. You have to have an open mind over where to attack.

“If you get it right you’ll win, if you don’t you won’t – it’s as simple as that.

“We’re pretty evenly matched in all departments. Australia aren’t much bigger than us and they don’t have an advantage in speed.

“They’re a very skilful team which is tactically well aware and the game will be won on tactics.”

O’Sullivan insisted the selection of Ulster scrum-half Boss, who will make his full Test debut with Peter Stringer dropping to the bench, would enhance his side’s attacking options.

“Isaac is a more robust player than Stringer in some ways. He’s more aggressive around the fringes. He likes to run and take on the back row in scrums and is a threat,” he said.

“It took him a while to settle at Ulster but this season he has been very effective. He’s fought his way in on form.

“The team won’t change the game-plan because we have a new half-back. There’s not that much difference between him and Peter.”

Boss was born in New Zealand and represented the All Blacks at under-19 level but qualifies for Ireland through a maternal grandmother.

The 26-year-old former Hurricanes half-back, who will win his fourth cap on Sunday, said: “I’m delighted that I was in the 22 last week and to get the start this week is brilliant.

“I can’t wait for Sunday to come. Hopefully I’ll put in a good performance. The squad is very confident after beating South Africa but we’re not getting above ourselves.

“We know we can play well in areas and we’ll have to lift our game for Australia.

“I know a lot about them from playing Super 12 rugby and hopefully we can stem the tide of their attacks. They’re pretty good when they have the ball in hand.”

Boss’ Ulster team-mate Young will also make his full debut following three substitute appearances, with Marcus Horan dropping down to the bench.

Girvan Dempsey has been replaced by Murphy at full-back while Hickie comes in for Andrew Trimble who is still troubled by a recurring hamstring problem.

“Andrew got a really bad knock on the summer tour over his knee. He had quite a bit of bruising and spent a lot of time rehabbing it,” said O’Sullivan.

“His pre-season in terms of building power in his legs was truncated. He isn’t completely up to where he needs to be in that respect. The spin off is that he’s fatiguing in games.

“The hamstring isn’t damaged, it’s fatiguing. It gets tight and sore and if he runs on it there’s a chance he’ll rupture it. A fella like Andrew who runs so quickly means it’s high risk to run on it.

“So we’re just being careful and taking precautions. We could play him against Australia but he could fatigue again and we’re worried he might break down.”