Algebraic maps and morphisms

Question

Let $X,Y$ be two projective varieties (irreducible). A map $f\colon X\longrightarrow Y$ is called continuos algebraic map if its graph $\Gamma(f)\subseteq X\times Y$ is an algebraic set. I'm trying to check that there exists an open $U\subseteq X$, such that $f_{|U}$ is a morphism. Any help?