Without saying as much, the Australians expected Saturday's game at Hull would be a mere formality ahead of an anticipated clash with New Zealand in the final.
But the Lions surprised everyone, including most of their critics and supporters, by thrashing the in-form Kiwis 38-12 with a performance and scoreline that hoisted them right back into Tri-Nations title battle.
Among several possible ramifications from this final round robin match, Australia can lose by seven points and still make the final.
But any more than that margin and the reigning champions can pack their bags a week earlier than anyone would have imagined while Great Britain and New Zealand play the crown.
"It's game on now," said Buderus as the tourists arrived back in the north of England after Saturday's 44-14 win in the one-off test against France in Perpignan.
"There's a few scenarios this weekend depending on which way the result goes.
"It won't be a relaxed week for us this week, it's a must win game.
"Our preparation now has to be first class."
Trent Barrett is desperate to play after a frustrating time battling an old foot injury which has required intensive physio and lots of cross training.
Despite facing a fitness test he's extremely confident he can take on Great Britain on Saturday after a Paris orthopedic specialist made special inserts for his boots to balance his feet better and help reduce the pain.
"It's an old injury which just got stirred up," said Barrett whose size would be an asset at five eighth in the injury-enforced absence of Darren Lockyer.
"I've stayed off it for a week and it's feeling pretty good.
"The insert takes some pressure off the part of the foot that is sore.
"When it plays up, it plays up a fair bit and is very sore.
"But I'll definitely be right, I'll definitely play if I'm selected.
"It's a huge game, if we lose, we're a big chance of missing out on the final.
"But we can put all that for and against stuff out of their control if we win."
Coach Wayne Bennett would have expected to have this week to continue preparing his side to defend its title.
But he now has to get them to peak a week earlier with Australia's long reign as the world's best under direct threat.
He'll have to decide, if Barrett plays, whether to stick with experienced Penrith warhorse Craig Gower at half, or return rookie Scott Prince to the No.7 jumper after he played five-eighth against France.
"Gowie and Princie both played pretty well the other night," said Barrett staying neutral on the selection dilemma.
"Neither of them have done anything wrong and hopefully I'm in there somewhere and I'm really looking forward to it."
Lions coach Brian Noble, somewhat of a sudden death specialist having guided Bradford through four knockout games to win the Super League final, described the clash with Australia as "Russian roulette".
"It's the same scenario for us this week as it was last week. We've got to win the game and to do that against Australia we've got to raise the bar again," he said.
Great Britain's win came at a cost, with halfback Paul Deacon (face) ruled out for the rest of the series, and fullback Paul Wellens (knee) and winger Brian Carney (hamstring) in doubt for the clash with the Kangaroos.
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