Wry expression from serious expert (7)
I believe the answer is:
grimace
'wry expression' is the definition.
(I've seen this before)
'serious expert' is the wordplay.
'serious' becomes 'grim'.
'expert' becomes 'ace' (ace is a kind of expert).
'grim'+'ace'='GRIMACE'
'from' acts as a link.
(Other definitions for grimace that I've seen before include "Expression of distaste" , "Wry look" , "Contort the face" , "Express wry amusement" , "Glower" .)