in part due to a thumb injury.

The Serb then made the flight to Beijing, China for the Olympics only to withdraw with the lingering thumb injury.

Ivanovic began the year on a high note upsetting Wimbledon champion Venus Williams of the USA at the Australian Open quarterfinals before falling to the eventual winner Maria Sharapova of Russia in the final. A win in Indian Wells gave Ivanovic her first title of the year.

At New York however in her opening round match, Ivanovic struggled with unforced errors and failed to display any form befitting a world number one player. She would manage to win in three sets but could not repeat the struggle win today as she would lose 6-3, 4-6, 6-2 to 188th ranked Julie Coin of France.

After the match Ivanovic admitted she did not play like a world number one.

"This was a very, very disappointing loss for me. I really struggled and made too many unforced errors and my serve was not working really well. Obviously, it’s very frustrating because I know I can play so much better,” Ivanovic said.

"Obviously if you would ask me at the moment if I’m playing like number one, probably not, but I can’t judge too much on that because I really haven’t had (a) chance to practice. This kind of loss I had today is just incentive to work harder, to go back on the court and to keep working hard and practising and improving.”

The shocking defeat was the earliest loss by a US Open top seed since 1968 and meant that several other WTA Tour players would have a greater chance at the world's top ranking. Serena Williams of the USA, Jelena Jankovic of Serbia and the Russians Elena Dementieva and Dinara Safina all could possibly reach the number one spot with a US Open title win.