The look on Grigor Dimitrov's face says it all.

It's not often that someone gets one over on legendary tennis player and 17-time Grand Slam champion Roger Federer, so it's a bit of a big deal when it happens. And even more so when the person achieving it happens to be a little kid.

Federer and Dimitrov were playing an exhibition match for World Tennis Day in New York's Madison Square Garden when Dimitrov followed one of the expo's traditions by bringing on a young fan from the crowd to play a point in the third set, but no one expected what was going to happen next.

Dimitrov may be laughing now, but he won't be when that kid is coming for his titles in a few years.

Via YouTube/