To enter suddenly: one prestige vehicle up first time (6)
I believe the answer is:
irrupt
'to enter' is the definition.
(irrupting is a kind of entering)
'suddenly one prestige vehicle up first time' is the wordplay.
'suddenly one prestige vehicle' becomes 'irr' (I can't justify this - if you can you should give a lot more credence to this answer).
'first time' becomes 't' (ist letter of 'time').
'irr'+'up'+'t'='IRRUPT'
Can you help me to learn more?
(Other definitions for irrupt that I've seen before include "Break, rush, in" , "Enter forcibly and suddenly" , "Enter forcibly or violently" .)