The Lions edged out the Wallabies 23-21 in Brisbane to win the first Test, only for the hosts to hit back seven days later and claim a 16-15 victory in Melbourne.
However attention now turns to Sydney - with the Lions desperate for a first series win in 16 years, while Australia are looking to repeat their 2001 triumph.
Lions head coach Warren Gatland has rung the changes to his line-up - including the controversial axing of Brian O'Driscoll.
Australia counterpart Robbie Deans, though, has made just one change - with George Smith making a surprise return.
And ahead of the decider, we bring you all the latest news, views, video and opinion.
Australia v Lions: Preview
After 720 minutes of rugby the British and Irish Lions' tour now hangs on one game against Australia in Sydney on Saturday. The main talking points heading into the clash have surrounded the two surviving playing members of the '01 series - Brian O'Driscoll and George Smith. O'Driscoll, a veteran of four tours, will have to watch the match from the stands at the ANZ Stadium after he was dropped, while Australia flanker Smith has been handed a sensational recall nearly four years after he last appeared on the international stage.
Gatland - It is the right call
Lions head coach Warren Gatland is adamant his bold choice to drop centre Brian O'Driscoll for the final Test is the right decision. He said: ""I have to put hand on my heart and say it's the right rugby decision. I would hate to think we had made calls on trying to avoid criticism or public favour or perception. He has been a big part of the story of this tour. He played in the first two Tests and he has been a part of a win and a loss. He is obviously very, very disappointed, as any player would be, but it's like everything, it's a learning process."
Deans - We're very confident
Australia head coach Robbie Deans claims his side are "confident" of claiming a series-deciding victory over the Lions at the ANZ Stadium on Saturday. He said: "We can honestly say we haven't played our best footy throughout the series thus far and probably made too many errors to give ourselves an opportunity to play any sort of fast, flowing rugby. We were able to do that in the last 20-30 minutes in the Test in Melbourne and the thing is we will take a lot of confidence out of that moving forward and we have to make sure that we start well."
Rowntree - Our biggest game
Assistant coach Graham Rowntree insists the British and Irish Lions are "ready for this battle" ahead of Saturday's series decider against Australia. "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," he said. "There's one huge performance left in us. These players are desperate for tomorrow. We have to go out and give it everything. This is the biggest game of our lives, as players and coaches."
End of an era
In his final Lions Diary, Miles Harrison previews the decisive Test and reflects on the dropping of Brian O'Driscoll. "I have spoken to ex-players who would have done it and ex-players who would not have done it but Gatland is in the position where he is paid to get this right in the way he sees fit," said Harrison. "He does not want any regrets and 'if only' feelings when he boards that plane home. He is backing his judgement and that is what he is there to do. I am sure Brian O'Driscoll will understand all of that."
The Sky Sports pundits give their verdicts on the Lions line-up for the series decider against Australia. Former Wallabies wing David Campese said: "The changes have occurred because Gatland has panicked a bit. Six changes going into 80 minutes of rugby is a lot and the more you change, the harder the game is. The Wallabies have really got the same side and they've got the momentum. O'Driscoll is a great player but who will be the leaders for the Lions on Saturday? There isn't anybody anymore."
Sky Sports speaks to some of rugby's leading lights to get their verdicts on 'The Decider'. Former Lions prop - and current director of rugby at Wasps - Dai Young said: "The first two games have shown that there is nothing between these two teams. The first 30 minutes is going to be huge and I think it is the type of game where whoever gets their noses in front it is then going to be quite hard for the other team to turn it around. I think any 10-point gap is going to be very difficult to turn around."
Try your luck
Sky Sports presenter Alex Payne looks at the best bets for the crunch clash between the Lions and Australia at the ANZ Stadium. "If you want to go with your head and play the stats game, Australia are your bet; they have had the better of Gatland's Wales on the last eight occasions and know how to handle what's coming.," he said. "However, if you bet with your heart, and I am guilty of this, then you will believe that Gatland has got his key cog back in Jamie Roberts (13/2 anytime try scorer)."
Saturday's clash at the ANZ Stadium will not be the first time the British and Irish Lions have gone into the final Test with the series on the balance. The past two tours to Australia have gone right to the wire, while previous trips to South Africa and New Zealand have had their fair share of crunch clashes to wrap up the series. And ahead of the hugely-anticipated third Test in Sydney, we look back at some of the past series deciders the Lions have faced over the years.
Oh my BO'D
In a final twist to his long and distinguished career with the British and Irish Lions, Brian O'Driscoll is now unlikely to pull on the famous red jersey again - with the Irishman dropped for the series decider against Australia. It is the latest cruel blow during his 12-year association with the tourists from the home union - however it is arguably the one that will hurt the most. And following his omission Sky Sports rugby union writer Tony Curtis looks back at the Lions career of the legendary centre. For a look back at O'Driscoll's 12 years as a Lions in pictures, click here