But despite Ronaldo's absence, Fernando Santos' side led 2-0 in Braga on Monday, only to be pegged back by the determined visitors.
AC Milan striker Andre Silva headed Portugal into the lead and when Joao Mario fired home a 20-yard drive, a straightforward victory appeared to be on the cards.
But Nabil Maaloul's men had other ideas, reducing the deficit through a well-placed strike from Anice Badri in the 39th minute.
Amid a raft of second-half substitutions and shortly after a disallowed William Carvalho header, Tunisia then produced a scrappy equaliser through Fakhreddine Ben Youssef to claim an unlikely draw.
Saif-Eddine Khaoui slotted a first-time shot wide in the first minute as Tunisia made a bright start, but Ricardo Quaresma should have opened the scoring.
Goalkeeper Mouez Hassen hit a loose pass straight to the winger, whose first touch let him down, with a subsequent floated finish clearing the crossbar comfortably.
Portugal took the lead in the 22nd minute, though, as Quaresma made amends for his miss.
Quaresma beat his marker on the right wing and delivered a deep cross from which Andre Silva got up highest in the penalty area to send a fine header past Hassan's grasping right hand.
Khaoui almost levelled immediately but he missed the target again when picked out by Hamdi Nagguez's low centre from the right wing.
Joao Mario doubled Portugal's lead before the break, sending a tremendous rising drive into the roof of the net after Tunisia failed to fully clear a right-wing Bernardo Silva corner.
Tunisia replied in the 39th minute, however, Badri rifling past goalkeeper Anthony Lopes after the ball broke kindly for him on the edge of the Portugal area.
A brilliant jinking run from Bernardo Silva saw him hit the post after the break, with the rebound flashed wide of the post by the Manchester City playmaker after Joao Mario's effort was blocked by Hassan.
Portugal thought they had wrapped up victory when Quaresma's free-kick was headed in at the back post by Carvalho, only for the flag to be raised for offside, with the visitors then snatching the leveller in the 64th minute.
Ali Maaloul's cross found its way through to Ben Youssef in the box, the substitute striker getting just enough on his scrambled finish to beat Lopes and give Tunisia a huge boost in their World Cup preparations.
Substitute Goncalo Guedes fired wide but neither side looked likely to score a late winner as the match petered out.