Watch: Pro tennis match hilariously interrupted at crucial point by 'Cotton Eye Joe'

Tennis is a sophisticated sport, and there is a certain level of decorum that is expected when you attend a high-level match. 

The biggest rule for spectators — do not make noise when the ball is in play. People, with few exceptions, usually follow it. 

That peace and quiet was interrupted on Saturday afternoon in Montreal during a semifinal match at the National Bank Open in Montreal between Iga Swiatek and Jessica Pegula.

With Swiatek serving in an important second-set tiebreak, the popular stadium anthem song "Cotton Eye Joe" began suddenly playing over the court's PA system without any warning. It stunned everybody. 

It was not only an unbelievable interruption at a crucial moment in the match, but the most hilarious possible song that could have interrupted it.

Have a look.