An exaggeration on the part of Ventress, although she didn't do particularly poorly. I believe the duel takes place in The Defense of Kamino, but I might be wrong.
Anyway, Mace has her giving ground the entire duel, which doesn't last very long itself. He drives her to the edge of the cliff, from where she leaps onto a droid and escapes.
So no, Asaaj doesn't come "within a hair" of defeating Mace.