Morocco extended their record-breaking run of successive victories by a national team to 19. In October, they went past the previous best of 15, set by Spain from 2008-09.
It was a far from convincing showing, however, from highly fancied Morocco who are 97 places above the small Indian Ocean island nation in the world rankings and had to toil hard for the points in the rain at Rabat's Complexe Sportif Prince Moulay Abdellah on Sunday.
Morocco squandered an early penalty and were goalless at halftime despite dominating possession, eventually breaking the deadlock in the 55th minute when Noussair Mazraoui did well to keep the ball from going out of play before passing it square for Diaz to side-foot home.
El Kaabi scored a trademark bicycle kick goal in the 74th minute, 10 minutes after coming on as a substitute, to ease the tension.
Morocco looked initially to be labouring under a heavy burden of expectation and tiny Comoros comfortably held them at bay before the superior firepower of the hosts ensured victory.
The hosts could have been ahead as early as the 11th minute after a soft penalty awarded for a challenge by Iyad Mohamed on Diaz. But Soufiane Rahimi hit the spot kick straight down the middle, striking the knee of goalkeeper Yannick Pandor and watching the ball loop away to safety.
But they eventually broke down the resistance as Diaz got deserved rewards for his continual probing and El Kaabi's goal ensured a respectable scoreline.
Comoros had a chance for an equaliser four minutes after Diaz's goal but Rafiki Said shot straight at Morocco goalkeeper Yassine Bounou in their first chance of the match.
"The opening game is always difficult but we came good in the second half," said Morocco coach Walid Regragui.
There will be concern in the home camp, however, after captain Romain Saiss limped off after 18 minutes, with the centre back leaving the field in tears. He spent the first half of the year sidelined by ankle surgery and only last month returned to the national side after a year's absence.
