One's tied with Chelsea -- managed to let in nil (8)
I believe the answer is:
shoelace
'one's tied' is the definition.
(shoelaces get tied)
'chelsea managed to let in nil' is the wordplay.
'managed' indicates anagramming the letters.
'to let in' indicates putting letters inside.
'nil' becomes 'O' (O resembles 0).
'chelsea' is an anagram of 'shelace'.
'shelace' going around 'o' is 'SHOELACE'.
'with' acts as a link.
(Other definitions for shoelace that I've seen before include "Cord fastener for footwear" , "String for footwear" , "Tier on foot" , "Oxford tie?" , "What ends in aglets" .)