HFX-9 Power suddenly ceases with squeel-new pads needed?

I just started using a used set of HFX-9 Carbons, and things appear to be in great shape, with no rubbing issues, etc after several decent rides.
I did notice however, that my front brake, when really asked to bear down, starts out with awesome stopping power, then all of a sudden, starts to howl, and at the same time loses a good bit of grab. The MOMENT the howl starts, you can feel it lose grab on the rotor. Since these were used pads, can I assume that the front pads have been contaminated maybe? The lever does NOT suddenly pull in further, it just loses grab.