Speak indistinctly, losing marks at first, say (5)
I believe the answer is:
utter
'first say' is the definition.
'utter' can be an answer for 'say' (I've seen this before). I am unsure of the 'first' bit.
'speak indistinctly losing marks' is the wordplay.
'speak indistinctly' becomes 'mutter' (I've seen this before).
'losing' is a deletion indicator.
'marks' becomes 'm' (former German currency).
'mutter' with 'm' taken away is 'UTTER'.
'at' is the link.
Can you help me to learn more?
(Other definitions for utter that I've seen before include "Positive" , "Give voice" , "Say; total" , "Speak - out-and-out" , "Sheer" .)