Director Loncraine's lack of knowledge about the game also led him to offend the grande dame of tennis - and fail to spot the star potential of its hottest young player.
Bettany said: "[Loncraine] was off to do some research and he was introduced to Martina Navratilova, and he asked her what she did. She said: 'I don't mean to be rude but if you are going to make a film about tennis you really should know who I am.'"
And during casting, he turned down a young, blonde girl eager for a role because, according to Bettany, she looked too like Dunst. The girl was Maria Sharapova, now the tournament's reigning champion.
Bettany has admitted that casting non-players in the film "turned out to be stupid and a little arrogant".
"You go along and see these professionals play and they hit the ball so beautifully," he said.