Last week it was the Wallabies would made desperation work in their favour as they squared the series with the narrowest of wins in Melbourne.
But this time Rowntree says the shoe is on the other foot and that the Lions will leave no stone unturned in their quest to earn a place in the history books at the ANZ Stadium.
"Seeing how we've trained all week, crikey we're ready for this battle. We want this game tomorrow and the words I'd use is desperate," said Rowntree.
"We saw the reaction from Australia after they beat us - their captain James Horwill was crying. They threw everything at us and beat us by a point. We didn't get our game going and we know that. There's loads more to come from us and the guys are desperate to win.
"This is grand final rugby, the last throw of the dice with everything to play for. We have to go out and give it everything. This is the biggest games of our lives, as players and coaches. A lot of us have been involved in grand final games, but this is the biggest one for us.
"We've refreshed ourselves for a couple of days in Noosa, it was important to switch off after last week. We've restocked the team and made some changes."
The Lions will go into their final match of the 10-game tour without injured skipper Sam Warburton and veteran second row Paul O'Connell who are both injured, while quadruple tourist Brian O'Driscoll missed out on selection for the 23-man squad.
But all three have played an important role in this week's build up, complementing the thoughts of new captain Alun Wyn Jones who continues to hold the respect of his peers ahead of such a crucial encounter.
"They've spoken in most meetings and that's why we wanted them around," added Rowntree.
"Brian has been exemplary as the true professional that he is. That's was Wednesday's news, we move on and Brian's been fine with that. He's been leading the group still and helping the lads prepare. Alun Wyn has led the team very well and he has that respect among the players."
Rowntree admits that he expects another big battle up front, with the Lions having picked an even bigger pack than last week and the hosts having named just two backs on the bench.
The Lions forwards coach believes the Wallabies will try and stop his side at source but he didn't anticipate legendary flanker George Smith being at the heart of that Aussie onslaught.
"I'm surprised by that. He's been out for a long time and it will be interesting to see his match fitness. They've got three good sevens in that squad but what we've seen of him in the Super 15 is that he makes good decisions.
"He's still very good technically and makes good decisions on when to go into the breakdown. It will be a big challenge for Sean (O'Brien). I'm hoping his selection is a reflection of what we brought to the breakdown.
"You have to have a good pack, regardless of who you're playing against. They've picked a 6-2 bench so it's pretty evident how they want to take us on and nullify what we're doing. We've picked the appropriate pack for this game and have a strong bench to back it up. We're all good and ready to go."