grammatical number - 'One out of three people thinks' or 'one out of three people think'?

Could someone please explain to me which of these sentences is correct and why?

1. Only one out of three respondents (29%) thinks otherwise.


2. Only one out of three respondents (29%) think otherwise.

I understand that the subject of this sentence is singular, and therefore, theoretically, the verb should be singular, but this just doesn’t sound right.

Could someone please help?