Do better than (7)
(Other definitions for upstage that I've seen before include "(Of actor) away from the audience" , "Pugs eat (anag.)" , "Divert attention from another as actor might in play" , "Take the limelight from" , "moved away from the audience" .)
'do better than' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for outplay that I've seen before include "Act better" , "Defeat (sport)" , "Perform better than" , "Get the better of" , "As sportsperson, overcome" .)