usepackage{pgfplots}
pgfplotsset{compat=1.8}
begin{tikzpicture}
begin{axis}[domain=0:1,xmax=1,ymax=1,zmax=10,samples=50,
  unbounded coords=jump, filter point/.code={%
        pgfmathparse
          {pgfkeysvalueof{/data point/x} + pgfkeysvalueof{/data point/y} > 1.8}%
            ifpgfmathfloatcomparison
              pgfkeyssetvalue{/data point/x}{nan}%
            fi
          },
        ]
  addplot3[surf] {1/(1-x*y)};
end{axis}
end{tikzpicture}