relative positioning in multipart nodes

Question

Is there a way do draw a line from the beginning of the tip of the brace, using relative positioning?

\documentclass{article} 
\usepackage{tikz}
\usetikzlibrary{shapes.multipart,positioning,decorations.pathreplacing}

\begin{document}
   \begin{tikzpicture}
     \draw[help lines] (0,0) grid (3.0,3.0);
     \node[align=center,draw,shape=rectangle split,
           rectangle split horizontal,rectangle split parts=3, text width=2cm] (A)
           {1\nodepart{two}2\nodepart{three}3};
     \draw [decoration={brace,mirror,raise=5pt},
            decorate,below=10pt](A.one south) -- node[below=10pt]{}(A.two south);
     \draw [->] (-1.1,-0.5) --(-1.1,-2);
   \end{tikzpicture}
\end{document}

Answer 1

\documentclass{article} 
\usepackage{tikz}
\usetikzlibrary{shapes.multipart,positioning,decorations.pathreplacing}

\begin{document}
  \begin{tikzpicture}
  \draw[help lines] (0,0) grid (3.0,3.0);
  \node[align=center,draw,shape=rectangle split,
       rectangle split horizontal,
       rectangle split parts=3, text width=2cm] (A)
        {1\nodepart{two}2\nodepart{three}3};
  \draw [decoration={brace,mirror,raise=5pt},
         decorate,below=10pt](A.one south) -- coordinate[below=10pt] (tip) (A.two south);
  \draw [->] (tip) -- (2,-2);
  \end{tikzpicture}
\end{document}