Steal tray - managed to keep vigilant (4,5)

I believe the answer is:

stay alert

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'steal tray managed' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.

'keep vigilant' is the wordplay.
I cannot quite see how this works, but
'keep' could be 'stay' (I've seen this in another clue) and 'stay' is located in the answer.
'vigilant' could be 'alert' (similar in meaning) and 'alert' is present in the answer.
No letters remain.
This explanation may well be incorrect...

'to' acts as a link.

Can you help me to learn more?

I've seen this clue in The Daily Express.

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