Consider the following example sentence excerpted from Oxford Learner's Dictionaries:
One of the smaller parties came a close second (= nearly won).
Much to my surprise, the example sentence is placed under the adverb entry, rather than the noun entry, of second, by the authors of the authoritative dictionary.
I just wonder: If second here is an adverb, why is the article a in front of it?
Any help will be highly appreciated, thanks in advance.