The showpiece event kicked off 36 minutes later than originally intended following a total of three delays, with UEFA citing "late fans" as the reason for the disruption.
However, videos and eyewitness accounts displayed scenes of supporters being stranded outside locked gates for hours on end, with some appearing to jump the barriers as riot police used tear gas to try to quell the unrest.
The Reds began to assert control over the game during the opening exchanges, but it was a final for the ages for Thibaut Courtois, who was called into action straight away to keep out Mohamed Salah's near-post flick.
The Belgian then produced a phenomenal stop to tip Sadio Mane's effort onto the post in the 21st minute, and Liverpool would seemingly live to regret those missed chances at the end of the half when Karim Benzema poked home.
The goal was controversially chalked off for offside following a lengthy VAR review, with the ball deflecting into Benzema's path off Fabinho, but the Liverpool man's touch was not deemed as an intentional action.
There was to be no denying Brazilian starlet Vinicius on the stroke of the hour mark, though, as the 21-year-old peeled away from Trent Alexander-Arnold at the back post and slotted home from Federico Valverde's ball across.
Liverpool continued to huff and puff but there was no breaking down the impenetrable wall that was Courtois, who thwarted Salah at his near post and with a strong fist from distance before the Egyptian seemed certain to score in the 83rd minute.
Salah's delightful first touch allowed him to burst past Ferland Mendy, but Courtois was there again to stick out an arm before being mobbed by his teammates, and Real were presented with a gilt-edged chance to make it 2-0 in added time but substitute Dani Ceballos could not get the ball under control.
Nevertheless, Los Blancos held out to secure a 14th triumph in Europe's premier competition - completing a league and Champions League double in the process - as Carlo Ancelotti became the most successful manager in the tournament's history with four crowns.