Australia will be relying on Bernard Tomic.
Every team has a key player. We've seen Andy Murray and Novak Djokovic earn crucial wins for Great Britain and Serbia over the last few days, but it's not those stars who will ultimately decide their countries' Davis Cup fate.
The interesting part of Davis Cup matches is that the lesser-known players provide the excitement that settles each contest. It's almost guaranteed that the likes of Murray and Djokovic will emerge victorious in straight sets, so that removes a lot of the anticipation. They need to rely on their teammates—both in singles and doubles—in order to progress.
Three such teammates are listed below.
Bernard Tomic, Australia
Tomic and his team currently lead Poland 2-1, but it's still absolutely crucial that Tomic gets a win. The man standing in his way is Lukasz Kubot, who will be out to put the fixture to bed and see Poland advance.
Kubot is ranked at 70 in the world and is a very dangerous player. He reached the quarterfinals at Wimbledon this year and has beaten players ranked above him many times over the last couple of years.
However, Kubot was torn apart by Lleyton Hewitt in his previous match, so Tomic will be seeking advice from Hewitt on how best to exploit his weaknesses.
Australia would dearly love to return to the World Group, so expect Tomic to come out swinging early. If he gets on top of Kubot, he can run him off the court in a similar manner to Hewitt.
Alejandro Falla, Colombia
Colombia's match with Japan currently rests on a knife-edge at 2-2, so it will come down to Alejandro Falla. As the higher-ranked player, he will be expected to defeat Go Soeda, but it's going to be a nervy affair.
Falla ranked as high as 43 last year, but has since dropped back to 94. He was three points away from a straight-sets victory over Roger Federer at Wimbledon in 2010, but the Swiss master recovered to take the tie in five sets. Falla took Federer to the brink again at the Olympics in 2012, but again lost out in the final set.
Falla is a powerful player who can drag himself back into form over the course of a match, even if he is looking out of sorts. He won't stop going for his shots, and once he finds his range he can be very difficult to beat.
After a straight-sets loss to Kei Nishikori, he needs to raise his game. This is looking like the most interesting match before the final.
Vasek Pospisil, Canada
If we assume that Djokovic will triumph against Milos Raonic—which is by no means a given—Vasek Pospisil will be the man on whom Canada rest its hopes.
With the match balanced at 2-2, Pospisil will face Janko Tipsarevic. The Serbian is ranked 18 places above Pospisil and was as high as No. 8 last year. It's going to be an interesting battle. Tipsarevic has already played—and lost—a five-set marathon with Milos Raonic in this tie.
Tipsarevic remains the favourite, but the 23-year-old Canadian could spring an upset with consistent groundstrokes. He'll need to force Tipsarevic into mistakes—much as Djokovic did to Pospisil—but there's no denying he has the talent to do so.