Keeps up with us in blemishes (8)
I believe the answer is:
sustains
'keeps up' is the definition.
('sustain' can be a synonym of 'keep up')
'us in blemishes' is the wordplay.
'in' indicates putting letters inside.
'blemishes' becomes 'stains' (stain is a kind of blemish).
'us' inserted within 'stains' is 'SUSTAINS'.
'with' acts as a link.
(Other definitions for sustains that I've seen before include "It's Susan (anag.)" , "Nourishes or bolsters" , "Supports, keeps alive" , "Supports physically or mentally" , "Bears" .)