Number one, assess as excellent (5-4)
I believe the answer is:
first-rate
'excellent' is the definition.
(I've seen this before)
'number one assess' is the subsidiary indication.
'number one' becomes 'first' ('first' can be a synonym of 'number one').
'assess' becomes 'rate' (rating is a kind of assessing).
'first'+'rate'='firstrate'
'as' is the link.
(Other definitions for first-rate that I've seen before include "Top-class, excellent" , "Of the highest excellence" , "Stir after to be really excellent" , "Start fire to be really excellent" , "Prime" .)