Stretch certain to be riveted (10)
I believe the answer is:
spellbound
'be riveted' is the definition.
(both can mean fascinated)
'stretch certain' is the wordplay.
'stretch' becomes 'spell' (I've seen this in another clue).
'certain' becomes 'bound' (as in the phrase 'it's bound to be').
'spell'+'bound'='SPELLBOUND'
'to' acts as a link.
(Other definitions for spellbound that I've seen before include "Bewitched" , "Held rapt" , "appear hypnotised" , "Transfixed, mesmerised" , "frozen" .)