The striker was in superb form in the preliminary round first-leg encounter at the Stade Mohamed V stadium on Friday, as the Moroccan champions all but secured their progress to round one of the competition.
Iajour opened the scoring as early as the eight minute, before winger Abdelilah Hafidi doubled the advantage to give the hosts a two-goal cushion.
It took just one minute of the second half for Iajour to notch his second of the game, while Abdelkbir El Ouadi made it 4-0 nine minutes later.
Casablana were not done there, however, as Iajour added a fifth on 66 minutes before he completed the rout in the closing stages, leaving the Sierra Leone outfit with a seemingly impossible task in the second leg.
Elsewhere, Libyan outfit Al Ahli Benghazi put one foot in the first round with a 4-0 rout of Foullah Edifice at Stade Chedly-Zouiten.
Edward Sadomba put the hosts in front on 26 minutes, as the scores remained at 1-0 at half-time.
The Chad outfit surrendered under relentless Benghazi pressure in the second half, however, starting with Abdelrahman Fetori's penalty in the 55th minute.
With just under 20 minutes remaining Moataz Al Mehdi put the game beyond doubt, before Sadomba notched his second of the evening to complete the victory shortly before the full-time whistle.
Edifice now face a near-impossible task in recovering the tie in the second leg at the Stade Omnisports Idriss Mahamat Ouya.
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