Bencharki (C) celebrates the winner with his teammates (Photo: Zamalek s official Twitter account)
The Moroccan winger, who Zamalek are keen to extend his deal, notched what proved to be the winner two minutes into the second half as the Cairo giants put one foot in the Champions League group stage.
The result did not reflect Zamalek's superiority though, with the team wasting several easy chances after going ahead.
The game's first real opportunity fell to Tusker when Ibrahim Joshua headed just wide from a free kick on 29 minutes but it was then all Zamalek.
Bencarki missed a sitter on the stroke of halftime, mis-hitting his effort with the goal gaping after a pull-back from playmaker Youssef Ibrahim.
Midfielder Emam Ashour struck the woodwork with a fierce drive early in the second half before Bencharki, whose current contract runs out at the end of the season, atoned for his glaring miss to break the deadlock.
He collected a back-pass from Ibrahim and jinked into the area unopposed before wrong-footing the keeper from a tight angle with a left-foot shot that nestled into the far corner of the net.
Defender Mahmoud El-Wensh had a goal harshly disallowed for offside when he headed home on 64 minutes and winger Ahmed Zizo narrowly missed the target with an angled volley after a superb one-two with Ibrahim.
Ibrahim missed another clear-cut chance with nine minutes remaining when he broke clear following a threaded pass from Bencharki, only to see his tame shot blocked by keeper Brian Bwire.
Zamalek could have been punished for their wastefulness when Boniface Muchiri fired a low shot just wide in stoppage time but they breathed a sigh of relief following the final whistle.
They host Tusker in the second leg on Friday.
(For more sports news and updates, follow Ahram Online Sports on Twitter at @AO_Sports and on Facebook at AhramOnlineSports.)