Defending champions Zamalek missed out on a chance to close the gap on leaders Ahly after losing 1-0 at home to Ismaily in the Egyptian Premier League on Monday.
Succumbing to their second defeat under Scottish boss Alex McLeish, who took the helm late February, second-placed Zamalek are now nine points behind arch-rivals Ahly, who are on top with 50 points.
The winner by Ghanaian striker Banahene earned the Dervishes their 11th league victory this season, including a win over Zamalek by the same scoreline in Ismailia.
The game was by far an eventless affair.
Both teams remained toothless for the first 15 minutes until Zamalek showed slight superiority in terms of possession, thanks to pacey duo Ayman Hefni and Emmanuel Mayuka.
In the 26th minute, Zambian striker Mayuka came close to giving the hosts the lead but saw his close-range effort denied by Ismaily goalkeeper Mohamed Sobhy.
Banahene broke the deadlock three minutes past the half-hour mark when he latched onto an inch-perfect cross from Ahmd Samir, before skipping past his markers and slotting home from close range.
Zamalek intensified their efforts upfront to get the score level ahead of the interval, yet the coastal side's rearguard was too solid for the Cairo giants.
McLeish's men came with all guns blazing after the break, yet lacked cutting edge.
Near the hour mark, Ismaily replaced Banahene with skipper and veteran midfielder Hosni Abdrabou to get more control of the midfield.
McLeish shortly afterwards introduced striker Ahmed Mekki, replacing playmaker Shikabala in an attempt to increase firepower.
With 10 minutes remaining forward Mohamed Ibrahim made way for winger Ahmed Hmoudi, another substitution that didn't pay off for Zamalek.
Both teams fought fiercely in the dying minutes until the final whistle.
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