Ahly players celebrate the stoppage-time winner over US Monastir (Photo: Ahly s official Twitter account)
The central defender settled an otherwise slow-tempo affair with the last effort of the game, his superb looping header going over keeper Bechir Ben Said and into the net as Ahly took a first-leg advantage in the Champions League second preliminary round.
Earlier in the game, Ben Said pulled off two fine saves to thwart Ahly on a couple of occasions as the Red Devils dominated from the outset, although clear-cut chances were scarce.
Ahly gave new coach Marcel Koller, who took over following the sacking of Portuguese Ricardo Soares in late August, a winning start as the Cairo giants start their bid to make up for last season's loss to Moroccan side Wydad in the final of Africa's blue-riband club competition.
They will be favourites to book a place in the group stage when they host Monastir, who finished as runners-up in the Tunisian league last season, in the second leg in Cairo next weekend.
The fervent support of Monastir's passionate fans made for an exciting atmosphere but both sides looked lethargic, although Ahly were still the better side throughout.
The visitors had the lion's share of possession but mounted the only first-half threat after 16 minutes when Brazilian winger Bruno Savio, who showed flashes of his talent on his debut, headed straight at Ben Said when well-positioned to score following a free-kick.
Ahly kept the upper hand in the second period and went close via an angled shot from winger Ahmed Abdel-Kader, which Ben Said did well to parry.
The breakthrough finally came three minutes into the additional time when Abdel-Moneim sneaked between two markers to take full advantage of an inswinging free-kick from veteran left-back Ali Maaloul.
(For more sports news and updates, follow Ahram Online Sports on Twitter at @AO_Sports and on Facebook at AhramOnlineSports.)