Almost in the lead for a brief moment (6)
I believe the answer is:
second
This clue is a double definition.
'almost in the lead' is the first definition.
(one place behind first)
'brief moment' is the second definition.
(I've seen this before)
'for a' acts as a link.
(Other definitions for second that I've seen before include "Subordinate; moment" , "Moment; back" , "Support, assist" , "Next to first" , "Unit of time - after No 1" .)