With no Rafael Nadal, and with Novak Djokovic not showing the form of 12 months ago, could there be a winner of the US Open from outside the big three?

Although Roger Federer has gone back to the top of the rankings, the air of invincibility surrounding the top players looks to be fading.

The latest odds on Bet365 reckon that only two or three players can take full advantage at the final Grand Slam event of the year.

Away from Federer and Djokovic, Andy Murray looks like the best bet to claim the title in New York, where he was a finalist in 2008.

Murray will certainly have been boosted by his display at both Wimbledon, where he was beaten in the final, and the Olympics, where he won the gold medal with a win over Federer in a five-set match for the first time.

David Ferrer is another contender, especially after he was promoted to fourth seed, following Nadal’s withdrawal through injury.

The Spaniard, described as the best returner in the game by Federer, is enjoying his best season to date, with one semi-final place and two quarter finals under his belt in 2012.

A former Flushing Meadows winner also looks a serious threat to take the title, with a welcome return to form for Juan Martin del Potro.

The 23-year-old caused a big upset when lifting the trophy in 2009, defeating Nadal in the semi-finals before beating defending champion, Federer, in the final.

The Argentinian then spent much of 2010 on the sidelines with a serious shoulder injury and it has taken him time to get back to somewhere near his best.

Del Potro has already reached two Grand Slam quarterfinals this year, and his victory over Djokovic in the Olympic bronze-medal match showed he is once again a real threat.

Fans thinking of placing a bet on sports  should be aware that Djokovic is the current favourite for the US Open title, followed by Federer and Murray.