Best, strange as it seems (5)

I believe the answer is:

worst

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

I can't explain the rest of the clue.

(Other definitions for worst that I've seen before include "Strangely, best" , "Least well" , "Best; least good" , "Most severe" , "Get better of; very bad" .)

I've seen this clue in The Globe and Mail.

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