At regular intervals, watched champion (3)
I believe the answer is:
ace
'champion' is the definition.
(thesaurus)
'at regular intervals watched' is the wordplay.
'at regular intervals' means one should take alternating letters.
The alternate letters of 'watched' are 'ACE'.
(Other definitions for ace that I've seen before include "smashing" , "even higher than the king" , "star" , "Brill" , "Top playing card" .)