Positive review from an additional (third) reviewer (endorsing the 2nd reviewer) against a negative review from the 1st reviewer
It would be strange for the editor to solicit the third review and then not even consider it: that sounds like a waste of at least three people's time.  However, as to how this will affect the final decision: as Nate Eldredge points out, the editor is not obligated to go with two out of three.  In fact an editor may go against the recommendations of all the reviewers, and this certainly happens sometimes, especially in our day in which so many journals have "very high standards."  

Buffy says "Anything here would be a guess."  I agree, and here is my guess: if the editor solicits a third review and the third review is really positive, then the editor is likely to accept your paper unless the first reviewer comes up with new, relevant, significant negative comments.  (Why?  Because, again, the editor could just as easily -- and in fact, more easily -- have rejected your paper after the first two reviews.)  

However, in some hard-nosed decision theoretic sense, you don't need to know the answer to this question, by which I mean to say that you will find out eventually and until then you have done the optimal thing.  If that doesn't cheer you up: look, if two out of three reviewers are really enthusiastic about your paper, then even if this journal doesn't accept it, some other, similar journal probably will.  Congratulations on your good work.