The Morocco fans gave the match a vintage World Cup feel in a boiling atmosphere at the Al Thumama Stadium and Sabiri curled a wide free kick past Thibaut Courtois before Aboukhlal netted in stoppage time to put Morocco top of Group F with four points, one ahead of Belgium.
It was Morocco's first win at a World Cup since they beat Scotland in 1998. They left the 2018 tournament with a single point.
Belgium, who had scraped a 1-0 win over Canada in their opening game, again looked a pale shadow of the team who finished third in 2018 and climbed to second in the world rankings. They must now battle for a last-16 spot against Croatia.
The Red Devils' poor display even forced coach Roberto Martinez to send Romelu Lukaku on for the last 10 minutes in a desperate attempt to salvage a point, even though the burly striker had been struggling with a hamstring problem.
Croatia, who have a point from their draw with Morocco, play Canada in the other Group F game later on Sunday.
In a lively start, Morocco looked happy to sit and wait amid the deafening whistles of their fans, although bouts of intense pressing led to a couple of dangerous counter-attacks with Hakim Ziyech the main threat.
As Belgium's Kevin De Bruyne struggled to find his range and Eden Hazard remained largely ineffective, Morocco looked safe.
Courtois was beaten for the first time in the tournament when Ziyech fired a free kick into the pack and it bounced past the keeper at the near post on the stroke of halftime.
Romain Saiss, however, was marginally offside and referee Carlos Ramos ruled the goal out after a VAR review as the Besiktas defender was obstructing Courtois' view.
Morocco started to fancy their chances and were more on the attack with Sofiane Boufal's shot from just inside the box going just wide after the break.
Belgium were out of sorts and Martinez sent Youri Tielemans and Dries Mertens on to replace Amadou Onana and Eden Hazard.
Mertens had an immediate impact, forcing El Kajoui, who stood in minutes before kickoff for Yassine Bounou, into a superb save with a fierce shot.
Morocco substitute Sabiri broke the deadlock in the 73rd with an angled free kick similar to the one that led to the ruled-out goal in the first half, as Courtois could only fumble the ball into the net.
Saiss was also in the way, but onside this time, and Morocco defended tooth and nail until they found another opening, with Aboukhlal clipping Ziyech's cross into the roof of the net as the stadium boiled over. (Reporting by Julien Pretot; Editing by Ed Osmond)