Performs exceptionally well (6)
I believe the answer is:
excels
'performs exceptionally well' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for excels that I've seen before include "Does extremely well, shines" , "Does extremely well, better than most" , "Does very well, outshines" , "Performs exceptionally well" , "Does exceedingly well" .)