The dramatic climax followed a rare public campaign to save the life of Balal, who, at 19, killed another young man, Abdollah Hosseinzadeh, in a street fight with a knife back in 2007.
In an application of the sharia law of retribution, the victim’s family were to participate in Balal’s punishment by pushing the chair on which he stood.
Shargh newspaper said police officers led Balal to a public execution site in the northern city of Nowshahr as a large crowd gathering this week.
Samereh Alinejad, mother of the victim, who lost another son in a motorbike accident four years ago, asked the crowd whether they know "how difficult it is to live in an empty house".
Balal, black-hooded and standing on a chair before a makeshift gallows, had the noose around his neck when Alinejad approached him.
She slapped him in the face and removed the rope from his neck, assisted by her husband, Abdolghani Hosseinzadeh, a former professional footballer.
"I am a believer. I had a dream in which my son told me that he was at peace and in a good place," she told Shargh. "After that, all my relatives, even my mother, put pressure on me to pardon the killer.
"The murderer was crying, asking for forgiveness. I slapped him in the face. That slap helped to calm me down.
"Now that I’ve forgiven him, I feel relieved."
What followed was more remarkable still. Balal’s mother hugged the grieving mother of the man her son had killed. They cried in each other’s arms — one because her son was killed, the other because hers was saved.
Afterwards, Balal said the "slap was the space between revenge and forgiveness".
"I’ve asked my friends not to carry knives… I wish someone had slapped me in the face when I wanted to carry one," Balal said in a television interview.
A high-profile campaign was launched by public figures including Adel Ferdosipour, a popular football commentator and TV show host, and former international football star Ali Daei, appealed for the victim’s family to forgive the killer.
According to the UN, more than 170 people have been executed in the Islamic republic since the beginning of 2014.
Under the country’s interpretation of Islamic sharia laws in force since a 1979 revolution, murder and several other crimes are punishable by death.
However, the victim’s family has the right to spare a convict’s life in return for blood money, under Islamic laws.