Narrowing your search terms to just the one post is also helpful in situations where the site doesn't autogroup properly. For example, searching against the REQ number if the post has one.
But I'd imagine that autoselecting wouldn't be that helpful for most search engines, since the number of results that can be displayed per page is limited. So in a situation where it would be worth autoselecting (i.e. with lots of mixed up results), it's likely that the results you need would be spread across many pages anyway. So narrowing your search and using the filters (including date, poster, etc) would probably work out better.