I’ve looked up the latest version of the wp search query, it looks like it was changed a bit since the last time.
It appears to be using and ‘and’ type of logic (so all keywords must match) and there is some relevance as well. In this case try:
– On the General Options -> Behavior panel changing the keyword logic to ‘AND’ instead of the ‘OR’: http://i.imgur.com/jVkGh7F.png
– On the Ordering panel changing it back to the default: http://i.imgur.com/4XZ5olI.png
I tried a few queries on my test environment, and got very similar results with this configuration.