Over 1,000 Algerians, who had flown in during the day from Algeria, as well as several hundred Egyptians could be heard loudly throughout the game at the Ombaka Stadium Thursday as they were beating drums and cheering for their side.
The goals for the Pharaohs were scored by Abdrabou Hosni, who scored a first-half penalty in the 39th minute which led to Rafik Halliche being sent off, while Mohamed Zidan scored his side's second in the 65th minute.
Mohamed Abdelshafi added a third in the 81st minute when he found the back of the net from an acute angle. In injury time Mohamed Nagui scored his side's fourth to take his personal tally for the tournament to four.
The Algerians ended the game with eight players after Nadir Belhadj was sent off in the second half for a two-legged tackle on Ahmed Al Muhammad and goalkeeper Faouzi Chaouchi followed him for an early shower three minutes from the end for trying to kick out at Nagui.
The opening goal of the game came directly after an Algerian corner, when an Egyptian break comprising two passes saw Algerian defender Rafik Halliche kick over the ball, which ran through to Emad Motaeb.
Although Halliche tried his best to dispossess Motaeb, he could only do so with a foul in the area and Benin referee Koffi Codjia pointed to the spot.
The Algerian players argued with the referee, leading to Halliche receiving his marching orders for a second booking.
Once all the tumult had died down, Hosni stepped up to take the penalty scoring into the left corner after waiting for a split second to see which way the goalkeeper would commit himself.
This hesitation led to further remonstrations with the referee and Chaouchi, who ran well over 40 metres to confront the referee and then slapped out at a team-mate who tried to hold him back, was booked.
Being a man and a goal down was always going to be a huge task for the Desert Foxes to come back and the Pharaohs completely dominated proceedings in the second half.
Zidan, who had earlier said that any game between the two sides was like a war, scored with a beautiful shot into the top corner from the edge of the area midway through the second half.
The goal took any composure that the Algerians still had at that stage out of them and two further goals and two red cards were the result.
Belhadj quite deservedly was sent off in the 70th minute after his lunging tackle.
Playing against nine men at that stage, the Egyptians capitalised on their numerical advantage and added a third in the 81st minute through Zidan Abdelshafi.
Worse was to follow for the World Cup finalist, who had Chaouchi sent off with three minutes to go before Nagy added a third.
The two sides were in November involved in a controversial World Cup qualifying campaign, which led to a play-off, which Algeria won 1-0 in Sudan. There were violent clashes in Algeria and Egypt after the match.
The victory sees Egypt extend their unbeaten run at the Africa Cup of Nations to 18 matches and they could become the first country to win three titles in a row on Sunday in Luanda if they manage to beat Ghana's Black Stars, who beat Nigeria through an Asamoah Gyan goal in the other semi-final played in Luanda.
Algeria will contest the third place play-off against Nigeria in Benguela on Saturday.