Local papers splashed photos of Saied and Karoui across their front pages on Monday.
“Political earthquake,” read the headline of Arabic language Echourouk newspaper, while Francophone Le Temps entitled its editorial “The Slap”.
The result was a major upset for Tunisia’s political establishment, in place since the uprising eight years ago that removed President Zine El Abidine Ben Ali.
It could usher in a period of uncertainty for the fledgeling North African democracy, the sole success story of the Arab Spring revolts.
ISIE reported low turnout at 45 percent, down from 64 percent in the country’s first democratic polls in 2014.
“The abstention was a sign of a rejection of the system rather than disinterest,” said political scientist Hamza Meddeb.
“People are fed up with a political class which failed to respond to their economic and social expectations.”
Late Sunday, Chahed urged liberals and centrists to unite for legislative elections set for October 6, saying low participation was “bad for the democratic transition”.