Is it Public Sector company or in Private sector ???
In Pvt sector, there is no compulsion to be fair or "appear to be fair" !!
So, one can go ahead even with one candidate who has 'passed' the written exam - it is another matter if the written exam had been designed with high difficulty level and the answers/hints have been provided to the only successful candidate.
These are exactly the kind of charges - of favouritism, or foul-play - that are sought to be prevented in a PSU; and there would have been a re-examination.
However, if you are in private sector; you also have the liberty to relax the passing standards in the written exam, so that you can call in more candidates.
This is the established practice; and is done even during Campus placement. Discuss with your seniors and take their approval before you proceed.
Warm regards.