The three top players are Roger Federer, Novak Djokovic and Andy Murray. The overall favourite until recently was Roger Federer. He is due to play Andy Murray in the semi-finals tomorrow (25 January 2013). However, Murray is also a very strong contender, and if he manages to beat Federer tomorrow he could well become the favourite to win. Federer beat Murray after a very tough match at Wimbledon in 2012, but the two are very closely matched and it will be interesting to see tomorrow's outcome.
Whoever wins this match will play against Novak Djokovic in the final on 27 Jan. Djokovic, who is the world number one, has just beaten David Ferrer in the semi-final. This has changed the odds, making Djokovic the current favourite - but the odds keep changing. You can find the latest odds here.