Successes as United start to press Son (3)
I believe the answer is:
ups
'successes' is the definition.
(I've seen this before)
'united start to press son' is the wordplay.
'united' becomes 'U' (as in Man U, English football team).
'start to' indicates taking the first letters.
The initial letters of 'press son' is 'ps'.
'u'+'ps'='UPS'
'as' acts as a link.
(Other definitions for ups that I've seen before include "successes" , "peak times?" , "Positive phases of the cycle" , "Increases (a level)" , "Highs" .)