Bottom, giving no thought to one’s performance? (4-2-3-5)
I believe the answer is:
seat-of-the-pants
'performance?' is the definition.
I don't know anything about this answer so I can't tell whether this works.
'bottom giving no thought to one's' is the wordplay.
I cannot really understand how this works, but
'bottom' could be 'sea' (sea bottom is a kind of bottom) and 'sea' is present in the answer.
'no' could be 'o' (resembles 0 - 'no' can mean 'zero') and 'o' is found in the answer.
'one' could be 'the' (both can introduce a definite example of something) and 'the' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Another definition for seat-of-the-pants that I've seen is " Instinctive".)