"I do not want any victims and clashes between police and innocent people," Petrosian said.
"That is why I am asking you to leave."
The police said eight people had died in clashes between security forces and the protesters in the capital.
For the past 10 days opposition supporters camped in Yerevan's Freedom Square in protest against the poll.
Protesters defied a police crackdown just hours after the police dispersed another rally and put Petrosian under house arrest.
Petrosian said earlier: "I am confined to my residence. Permission or no permission, we will press ahead with protests, because rallies and marches can only be banned when there is a state of emergency."
The protesters called for a new vote, alleging Serzh Sarkisian, the current president and former prime minister, had rigged the election.
Arman Musinian, a spokesman for Petrosian's party, said that among those arrested was former prime minister Hrant Bagratian.
Earlier on Saturday, Pertosian told reporters: "I am deeply convinced that even if Sarkisan stays on, he won't be a legitimate president. I have no doubt the people won't tolerate this."
Petrosian had contested the presidential polls with a mandate against corruption and has since alleged massive fraud in the elections that replaced Robert Kocharian, the former Armenian president.
The opposition has long accused Sarkisian of having used state resources to promote his candidacy, with the support of Kocharian.
Observers from the Organisation for Security and Co-operation in Europe (OSCE) have said that the election had mostly met international standards.
Ilkka Kanerva, the current chairman of OSCE and the Finnish foreign minister, has condemned the use of force against peaceful demonstrators.
Kanerva said: "I urge the authorities to use maximum restraint. I am troubled that there are reports of casualties and I urge the authorities to release those detained.
"I again call on the government and the opposition to engage in a dialogue."
Kocharian, the former president has described the protests as an attempt to grab power illegally and promised that the government's response would be "decisive and firm".