  We prove that Borel QCD sum rules for heavy-light currents yield very strong
correlations between the $b$-quark mass $m_b$ and the $B$-meson decay constant
$f_B$, namely, $\delta f_B/f_B\approx -8\,\delta m_b/m_b$. This fact opens the
possibility of an accurate sum-rule extraction of $m_b$ by using $f_B$ as
input. Combining precise lattice QCD determinations of $f_B$ with our sum-rule
analysis based on the three-loop $O(\alpha_s^2)$ heavy-light correlation
function leads to $\bar{m}_b(\bar{m}_b)=(4.247\pm0.034)\;\mbox{GeV}$.
