Create document via bulk vs index api

I'd like to know. Which is better performance using between bulk load and index?
It is clearly that it has better performance we index some/many documents from bulk api.
How about index 1 document from using bulk and index?

Bulk Load: https://www.elastic.co/guide/en/elasticsearch/reference/current/docs-bulk.html
index: https://www.elastic.co/guide/en/elasticsearch/reference/current/docs-index_.html

I would expect very little difference in that case.