Nervous, performing with advantage (2,4)
I believe the answer is:
on edge
'nervous' is the definition.
(on edge can mean nervous or tense)
'performing with advantage' is the wordplay.
'performing' becomes 'on' (as in being on stage).
'with' says to put letters next to each other.
'advantage' becomes 'edge' (having the edge is having an advantage).
'on'+'edge'='ON EDGE'
(Other definitions for on edge that I've seen before include "Highly strung" , "Apprehensive" , "Twitchy" , "Cliff-top walker may be" , "Tense and irritable, very nervous" .)