The 2013 ATP World Tour Finals are in full swing, and there are still a few underdogs in the field who could potentially surprise the top stars and win the tournament.
Rafael Nadal has secured the world's No. 1 ranking after defeating Stanislas Wawrinka on Wednesday, reports Piers Newbery of BBC Sport, but that doesn't necessarily mean he's a lock to win the tournament. Sure, it does guarantee him a spot in the semifinals, but he still needs to win two more matches against strong opponents to come out on top.
While the following underdogs are exceptionally talented players, they should be considered underdogs because of the fact that they are a tier below the likes of Nadal, Roger Federer and Novak Djokovic. With the bigger names in men's tennis always considered the favorites for every tournament, anybody not on their level is an underdog.
The following players have a real chance at making a run at the tournament title.
Juan Martin del Potro
On the opening night of the ATP World Tour Finals, Juan Martin del Potro won a fantastic match against Richard Gasquet. He came back from a set down to secure the victory and is scheduled to face Novak Djokovic on November 7.
The runner-up in 2009, del Potro has high expectations for this tournament, though he recognizes moving past Group B will be tough. Via Piers Newbery of BBC Sport: "Hopefully I can beat them [Novak Djokovic and Roger Federer] but it's going to be really tough for me. I don't have anything to lose against them."
The Argentine has had moderate success against Djokovic this year. He defeated him in the semi-finals of the ATP World Tour Masters 1000 Indian Wells, though he took the loss against him at the ATP World Tour Masters 100 Shanghai.
He and Federer have squared off just twice this year, and the two are even at one match apiece. Del Potro's victory came at Basel, where he won 7-6 (3), 2-6, 6-4.
Del Potro has history against the two aforementioned stars, but that's not the only reason why he should be considered a threat to steal the title away from them or the world's No. 1.
Del Potro's power-oriented game will work to his advantage against the likes of Djokovic. A powerful player, del Potro likes to smash the ball past his opponents. On an indoor surface, this works to his advantage. The ball will skip and pick up speed indoors, making it even more difficult for opponents to return his serves and strong forehands.
Don't be shocked if del Potro makes a serious run at the tournament finals.
With a defeat of David Ferrer, Tomas Berdych improved his chances of winning the tournament while ending the chances of his opponent's.
Berdych certainly didn't play a clean match against Ferrer, finishing with one more double-fault and 13 more unforced errors. His game was still good enough overall to win, but that's not the type of game he needs to be playing in the upcoming matches.
He plays Nadal next, and he'll have to be nearly flawless to take him down.
Regardless, the fact that Berdych was able to win while playing so poorly against a very good opponent bodes well for the Czech. If he can play a clean match against Nadal, then he stands a chance to upset him and move onto future rounds.
Against Ferrer, Berdych was smart in attempting to tire him out by making him move across the baseline. Having to constantly run back and forth to return the ball took a toll on Ferrer, and that ultimately played to Berdych's advantage.
While the same strategy may not work against future opponents, his ability to exploit the weaknesses of his opponents will. His intelligence of the game will work in his favor.
He and Wawrinka are both 1-1, so there's no guarantee that he'll advance just yet. That being said, he's a clear underdog given his win against Ferrer and ability to strategize against opponents.