The Lions must win at ANZ Stadium on Saturday if they are to secure their first series victory in 16 years - while Australia are looking to emulate their success from 2001, when they recovered from a Test down to win 2-1.
Ahead of the game, Sky Sports has sought the verdicts of six experts about what is likely to happen...
Wasps director of rugby - and former Lions prop - Dai Young
What has gone on before is irrelevant now. It is a one-off game and can go either way. 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. The referee will play a big part with his interpretation, while Leigh Halfpenny isn't going to miss too many with his kicking. If Australia are consistent as they were last week it is going to go right to the wire but it is going to be an exciting way to finish.
Bath director of rugby Gary Gold
A 17-all draw. I can't remember a Test match being more evenly balanced. From all my years being involved with the Springboks I am not sure I have witnessed anything like this. The back and forth selection changes, the balance of the game and who may or may not dominate and not a lot of people have talked about the influence of the French referee, that is going to be massive. I am not someone who sits on the fence. I do have a slight allegiance to the Lions brand if I am honest as I love the Lions, but I don't have an allegiance to any particular team and it is a brave man who starts making predictions. I would say the psychological battle is tipped towards Australia as they won the last Test but it is too close to call. It is going to be an epic Test match.
Saracens and England full-back Alex Goode
I would love the Lions to win. I think it would be great for the Lions and the whole tour. It is going to be a very tough Test, it has been a very long season for all the Lions and they need one last big push. I am disappointed and feel for Brian O'Driscoll. He has been the best player of his generation and the best player I have seen growing up. It is shame but hopefully the Lions will come away with a victory and that he can come away with a series win.
Bath and England centre Matt Banahan
I think the last two Tests will have really opened up the eyes of the Lions to what they need to do.
Gatland has selected a side to put in a massive performance and I think the Lions players know it is time to perform.
I think they will do and that they will finish on a high and get the win in Australia.
London Irish full-back Tom Homer
It has been a close series. Australia were unlucky to lose the first Test, then the Lions were a little unlucky not to win the second Test.
It has been down to the wire each time and I expect nothing less in the third Test. It could go either way.
I guess you'd say Australia have the momentum but it will definitely be a cracker.
Leicester and England centre Anthony Allen
I think Australia will win. I really don't want to say that and it is hard to say it but I think with the kicking ability that they have now, the discipline they have at the breakdown and their try-scoring ability that it will be Australia.
But it will be a narrow margin.