Won seat unexpectedly? You’re welcome! (2,5)
I believe the answer is:
no sweat
'you're welcome' is the definition.
I don't know anything about this answer so I can't tell whether this works.
'won seat unexpectedly?' is the wordplay.
'unexpectedly?' indicates anagramming the letters (I've seen 'unexpectedly' mean this).
'won'+'seat'='wonseat'
'wonseat' anagrammed gives 'NO SWEAT'.
Can you help me to learn more?
(Other definitions for no sweat that I've seen before include "Not a problem (US colloq.)" , "That won't be a problem" , "OK" , "in Australia with ease" , "It's not a problem (result of using antiperspirant?)" .)