Seeing less impressive performance (7)
I believe the answer is:
blinder
'performance' is the definition.
(I have seen 'Outstanding performance' mean 'blinder' so perhaps 'performance' could also mean 'blinder')
I can't explain the remainder of the clue.
(Other definitions for blinder that I've seen before include "Spectacular sporting performance" , "Spectacularly good sporting performance" , "Excellent piece of play" , "Star performance" , "the boy in "Equus"?" .)