Abdel-Maguid netted what proved to be the winner seven minutes before the break but Zamalek were also indebted to goalkeeper Mohamed Awad, who blocked a penalty on the stroke of halftime.
Moroccan winger Achraf Bencharki, a fan favourite who is likely to leave Zamalek later this month after his contract expired, was unlucky not to put the game to bed on at least two occasions in the second half.
But Zamalek still got the job done to continue their bid towards a second consecutive league title even though they could not make any new signings this season because of a transfer ban imposed by world governing body FIFA.
With Pyramids drawing 2-2 with Talae El-Geish, Zamalek moved four points ahead of the big-spending club in second. Ahly, who meet Future FC later on Tuesday, are nine points behind Zamalek but they still have three games in hand.
Contractors dropped to third from bottom with 20 points, two adrift of safety.
Awad's saves
Contractors had the better of the early exchanges and Karim Mostafa went close after eight minutes when his shot was deflected for a corner with the goal at his mercy after Awad could only parry a cross into his path.
Awad then kept the score goalless when he dived to his right to smother a goal-bound, low shot from Ahmed El-Sheemi from inside the area as Zamalek struggled to contain a wave of early attacks.
But Zamalek gradually grew into the game as Tunisian forward Seifeddine Jaziri sent a glancing header just wide following an inswinging corner from Zizo, who is the league's joint top scorer with 12 goals.
Another inviting corner from Zizo led to the opener on 37 minutes when Abdel-Maguid beat his marker to head home from eights yards out.
But the 21-year-old defender was powerless to stop a fast-paced breakaway just before the interval after Bencharki gave away possession in his own half.
Abdel-Maguid's mis-timed tackle brought down the pacy Luis Hinestroza but Awad easily saved Ahmed Ali's tame spot-kick and thwarted a follow-up effort with a brilliant stop.
It was all Zamalek in the second half as they dominated proceedings, with Contractors pegged back.
Bencharki broke clear after a threaded pass from Jaziri on 53 minutes but his cheeky chip narrowly missed the target.
Twelve minutes later, he was found unmarked by a superb cross from substitute Youssef Nabih but his far-post volley was brilliantly saved by Contractors keeper. The misses did not prove costly though as Zamalek held on for a precious win.
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