Campaign teams of incumbent Mohamed Moncef Marzouki and leader of Nidaa Tounes party Beji Caid Essebsi both announced victory in Sunday’s presidential election, claiming to have secured around 50 percent of the votes.
They also indicated that none of the two rival candidates managed to win enough votes to secure outright victory in the first round of the poll for the nation's top job.
The run-off will turn into a closely fought contest between the top two vote-getters Essibsi, who is seen as old guard who flourished under decades of autocratic rule, and Marzouki, a veteran opposition figure during Ben Ali’s era.
It will be the third election in three months in a country that has experienced democracy fatigue plagued by economic crisis, terrorist attacks and two political assassinations since the 2011 revolution.
Sunday's elections were marred by low youth voter turnout, a phenomenon widely blamed on political parties, which remain unable to engage the youth and address their issues.
Secularist and charismatic Beji Caid Essebsi, 87, is not was projected to win the run-off after his party Nidaa Tounes (Tunisian call) won last month’s parliamentary polls.
Essebsi served as minister of the interior, defence and foreign affairs under the country's founding president, Habib Bourguiba.
He was then parliamentary speaker under deposed former leader Ben Ali, which has led to critics accusing him of seeking to restore the old regime.
"Essebsi enjoys wide electoral support, backed by leftists and unionists. He also enjoys the support of the country's long-established elites and those wanting a return to a more orderly era," Mohamed Salah Ben Aissa, professor of Public Law at the University of Legal, Political and Social Sciences of Tunis told Al Jazeera.
Marzouki remains popular among supporters of Islamist party Ennahda, which did not field a candidate of its own.