Succeeded, came first, consuming oxygen, faint (5)
I believe the answer is:
swoon
'faint' is the definition.
(I know that faint can be written as swoon)
'succeeded came first consuming oxygen' is the wordplay.
'succeeded' becomes 's' (genealogical abbreviation).
'came first' becomes 'won' (I've seen this before).
'consuming' means one lot of letters goes inside another.
'oxygen' becomes 'O' (atomic symbol for oxygen).
'won' placed around 'o' is 'woon'.
's'+'woon'='SWOON'
(Other definitions for swoon that I've seen before include "Faint (with emotion)" , "Pass out" , "Lose consciousness" , "Display of extreme emotion" , "Show ecstasy" .)