Tennis Star Eugenie Bouchard -- I Wanna Date Justin Bieber!!!

Justin Bieber is being courted by a tennis superstar ... a 19-year-old phenom who declared her love for the pop star in front of a live crowd at the Australian Open.

The Belieber is Eugenie Bouchard -- a Canadian tennis star who just beat Ana Ivanovic and earned a spot into the A.O. semi-finals.

But in the moments after the match, Bouchard was asked ... for some bizarre reason ... if she could date ANYONE on the planet, who would it be.

Her response -- Bieber.

Eugenie's answer was met by a chorus of boos ... but she wasn't phased -- looking into the camera and saying, "Justin if you're watching ... heyyyy."