  We calculate the one-loop supersymmetric electroweak-like and QCD-like
corrections to the top-quark pair-production cross section at the Tevatron,
including the important effects of non-degenerate top-squarks and left-right
top-squark mixing. The largest electroweak effects yield a negative shift in
the cross section and are enhanced right below the threshold for top-quark
decay into top-squark and higgsino-like neutralino, and can be as large as
$-35\%$. The largest QCD effects are positive and are enhanced for light
top-squark masses, and can be as large as $20\%$. Such shifts greatly exceed
the present theoretical uncertainty in the Standard Model prediction, and
therefore may be experimentally observable. We also explore the one-loop shifts
in scenarios containing light top-squarks and higgsino-like neutralinos that
have been recently proposed to explain various apparent experimental anomalies.
