First vessel capsized (3)
I believe the answer is:
top
'first' is the definition.
(top can mean the best or first)
'vessel capsized' is the wordplay.
'vessel' becomes 'pot' (type of container).
'capsized' is a reversal indicator.
'pot' backwards is 'TOP'.
(Other definitions for top that I've seen before include "Surface" , "Highest point or position" , "SECOND PART OF 10 ACROSS" , "Summit, peak" , "Peak; child's toy" .)