Dean Melnyk and co-accused Andrew Brown -who pled guilty to murder last week - stabbed Kevin MacKay 27 times just hours after the funeral of 19-year-old Jamie Abba.
They are both facing life sentences. Judge Lord Armstrong deferred sentence until June when he will determine how many years they have to serve before being eligible to apply for parole.
Melnyk, 20, from Lockerbie, told jurors the he was "drunk and angry" when he and Brown, 23, went to the property on Peacock Place, Ecclefechan, on August 22 and attacked Mr MacKay.
During his trial Melnyk denied murdering Mr MacKay but admitted culpable homicide on the grounds of diminished responsibility. However the jury rejected the suggestion.