Blackout sees regulars leaving for capital (4)

I believe the answer is:

baku

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'for capital' is the definition.
(capital of Azerbaijan)

I don't understand the rest of the clue.

(Other definitions for baku that I've seen before include "Azerbaijan's capital" , "Capital city of Azerbaijan" , "Caspian Sea port" , "Capital of Azerbaijan on shore of Caspian Sea" .)

I've seen this clue in The Telegraph.

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