A see-saw North African showdown in Fayoum near Cairo was decided when Gaber scored seven minutes from time to give African newcomers Misr a 3-1 last
16 second leg triumph.
The Egyptians secured a place in the Thursday play-offs draw with a 3-2 aggregate victory having conceded a late goal to lose the first leg in Algeria.
A superb goal from Malagasy Paulin Voavy halved the second leg deficit for Constantine and nudged his club into an overall lead on away goals with 14 minutes to play.
Gaber then struck again to ensure an Egyptian presence in the play-offs of a competition won by Cairo giants Al Ahly two seasons ago.
Wael Farrag was another two-goal star for an Egyptian club, but his brace in Cairo could not prevent ENPPI being eliminated by Mounana of Gabon after a penalty shootout.
Both legs finished 2-0 in favour of the home team and the Libreville outfit won 5-4 on penalties to book a play-offs place for the first time.
Farrag scored early and late goals for ENPPI, who reached the semi-finals of the 2009 Confederation Cup.
Another close encounter ended with Kawkab Marrakech of Morocco using home advantage to edge Mouloudia Oran of Algeria 1-0 after a goalless first leg.
Mohamed Fakih settled the Maghreb derby after 34 minutes in Morocco, calmly converting a penalty.
There will be two Moroccan clubs among the 16 in the draw as 2010 Confederation Cup winners FUS Rabat qualified despite a 1-0 loss at Villa of Uganda.
This match was also settled by a spot-kick with Umar Kasumba converting a 55th-minute penalty in Kampala.
But it was a hollow victory for the East Africans after a 7-0 first leg drubbing in Rabat two weekends ago.
Medeama of Ghana reached the play-offs for the second time in three seasons by overcoming Al Ahly Shendy of Sudan 2-0 in Sekondi.
After a goalless first leg, Kwame Boahene broke the stalemate 27 minutes into the second leg and Abass Mohammed added a second goal soon after.
Tunisian outfits Esperance and Stade Gabesien, and Sagrada Esperanca of Angola qualified on Tuesday.
The eight Confederation Cup last 16 winners will be paired with CAF Champions League last 16 losers.
Tuesday, 19 April 2016
Sagrada Esperanca (Angola) 2-0 Vita Mokanda (Congo) (2-1)
Esperance (Tunisia) 3-0 Azam (Tanzania) (1-2)
Stade Gabesien (Tunisia) 3-0 Zanaco (Zambia) (1-1)
Wednesday, 20 April 2016
Kawkab Marrakech (Morocco) 1-0 MC Oran (Algeria) (0-0)
Misr Makkassa (Egypt) 3-1 Constantinois (Algeria) (0-1)
Medeama (Ghana) 2-0 Ahly Shandy (Sudan) (0-0)
SC Villa (Uganda) 1-0 FUS Rabat (0-7)
ENPPI (Egypt) 2-0 (4-5pen) Mounana (Gabon) (0-2)