Rafael Nadal and Novak Djokovic are facing off at the U.S. Open final Monday. Perhaps one of the most vibrant supporters in the sport is Djokovic's girlfriend Jelena Ristic.

The two, according to The Daily Mail, have been dating for about six years now and serve as one of the more entertaining tandems for fans.

Business Insider recently illustrated the many moods you can expect to see from Ristic as she watches her boyfriend play a tight match.

The Daily Mail reported the couple knew very early on they had something special. Ristic met the Serbian tennis star at Sport High School.

Ristic finished her Masters Degree with honors and, according to the report, is looking to procure her PhD in management.

In the meantime, she has her hands full as the director of the Novak Djokovic Foundation, an organization that helps "socially underprivileged" children and families in Serbia.

Tonight will mark the 37th meeting between Nadal and Djokovic -- the most in the Open era. It's also their third U.S. Open final; Nadal won in 2010 and Djokovic in 2011.