Luka Modric opened the scoring in the 14th minute, the 2018 Ballon d’Or winner curling a delightful shot past goalkeeper Khalid Eisa.
Marcos Llorente then produced a fine finish of his own on the hour mark for his first ever Real Madrid goal, firing in a low strike after the ball came to him following a Toni Kroos corner.
Skipper Sergio Ramos added a 79th-minute header from Modric’s cross, seven minutes before the United Arab Emirates champions registered a consolation through Tsukasa Shiotani.
The three-goal advantage was then restored in stoppage time via an own-goal from Yahia Nader.
It was a record fourth triumph in this competition for Real, with them surpassing LaLiga rivals Barcelona’s tally of three wins, as boss Santiago Solari celebrated his first trophy in management.
Early pressure from Solari’s men saw the ball deflect off an Al Ain post after Llorente sent a cross towards Lucas Vazquez, and Marcelo then drove a shot off-target.
Real subsequently survived a scare when Marcelo misjudged a header and Hussein El Shahat’s shot was kept out by Ramos on the line.
A minute later the Champions League winners were in front as Vazquez delivered the ball from the right, Karim Benzema touched it to Modric and the Croatia international curled a shot into the bottom corner from just outside the box.
Al Ain’s Caio put the ball in the Real net soon after but the effort was ruled out for offside, and for the rest of the first half it was one-way traffic as the Spanish giants looked to increase their advantage.
Vazquez, Gareth Bale and Benzema were all unsuccessful with shots and Ramos headed wide from a corner.
Benzema then failed to make the most of a good opportunity as he fired over, before Eisa did well to tip over a Bale header and save a Modric volley.
Bale, scorer of a hat-trick in the semi-final victory over Kashima Antlers, almost made it 2-0 in spectacular fashion shortly after the break, sending the ball just over with an overhead kick, and moments later a Benzema shot bounced wide.
Real then added a second when Al Ain’s attempt to clear a corner sent the ball to Llorente – who had just had a penalty appeal waved away – and the midfielder smashed it in, with the distance similar to how far out Modric had been.
Bale was thwarted by Eisa again and Thibaut Cortouis was called into action to deny Caio before Ramos connected with Modric’s delivery to make it 3-0.
Shiotani then reduced the deficit as he nodded in from a free-kick, only for Real to go 4-1 up in added time when substitute Vinicius Junior’s effort was inadvertently diverted in by fellow substitute Nader.