You had one night stand with someone else and unluckily next day you have found yourself in a possition to assess them in hiring process.
Oxford English dictonary says to the word:
one-night stand
1 informal: A sexual relationship lasting only one night.
1.1 A person with whom one has a one-night stand.
2 A single performance of a play or show in a particular place.
They did it just for the sexual intercourse, just to release stress or whatever. Nothing less, nothing more. I suppose so did you. I do not judge anyone of you; nobody should. Joe is going fishing, Pam is painting on glass and Brad watches wrestling. Shall we judge them for that?
What entitles you to claim that they are worse than you are? What exactly assures you that they will behave the same way in the workplace as they behaved in the bar?
Right now you are in the conflict of interrests. A big one. And any interferrence is bad interferrence and it can, and probably will, cost you more than just a reputation regarding your leisure time activities.
- They gets the job. You helped them because of the intercourse.
- They will be refused. You pushet them out because of the intercourse.
In both cases you mix your personal life and work life in unacceptable way. Maybe your intentions are good; but remember: The path to the Hell is paved with good intentions.
Pardon yourself from the whole hiring process. "I might be biased towards one of the candidates" is proper reasoning and it should be accepted without any problem. There is additional information (highly emotional and vulnereable to defend) on only one person in the scope. This information if unfair to the others; they didn't have the chance to neither succeed neither fail it this "test". Are you sure you would have better or worse feelings about them tha you have about this perticular one candidate?
If they are hired, talk to them and make consensus on what will follow this one-night stand.