With slight advantage, it could be a piece of cake! (5)
I believe the answer is:
wedge
'piece of cake' is the definition.
(I've seen this in another clue)
'with slight advantage' is the wordplay.
'with' becomes 'w' (abbreviation).
'slight advantage' becomes 'edge' (as in a competitor having the edge).
'w'+'edge'='WEDGE'
'it could be a' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for wedge that I've seen before include "Type of shoe" , "Splitting device" , "piece of cake" , "Tapering piece" , "Chock" .)