Nasty thirteen abash me simultaneously (2,3,4,6)
I believe the answer is:
in the same breath
'simultaneously' is the definition.
(I've seen this in another clue)
'nasty thirteen abash me' is the wordplay.
'nasty' is an anagram indicator.
'thirteen'+'abash'+'me'='thirteenabashme'
'thirteenabashme' anagrammed gives 'IN THE SAME BREATH'.
(Other definitions for in the same breath that I've seen before include "needing no further inspiration?" , "with a single blow?" , "Without breaking off" , "Together" .)