Switch on tea-maker for top performer (4,4)

I believe the answer is:

star turn

I'm a little stuck... Click here to teach me more about this clue!

'top performer' is the definition.
(I've seen this before)

'switch on tea-maker' is the wordplay.
'switch on' becomes 'start' (I can't justify this - if you can you should believe this answer much more).
'tea maker' becomes 'urn' (I've seen this before).
'start'+'urn'='STAR-TURN'

'for' acts as a link.

Can you help me to learn more?

(Other definitions for star turn that I've seen before include "Main act" , "Top performer" , "Most impressive act" , "Top of the bill" , "Leading act" .)

I've seen this clue in The Times.

Want a hint initially instead of a full solution? Install my app