The onus was very much on Real to force the issue against a notoriously well-organised Atlético outfit, and they duly broke the deadlock in emphatic fashion with just four minutes on the clock thanks to Rodrygo.
Federico Valverde - making his 300th Los Blancos appearance - fed the Brazilian, who made a darting run from the right before cutting inside the box and unleashing an unstoppable left-footed strike past Jan Oblak.
Atléti had to take a bolder approach, and Giuliano Simeone ought to have done better when he lashed wide from close range. The visitors’ response was encouraging, as Simeone surged his way past Brahim Díaz and flashed a ball across the face of goal that Valverde cleared away from the goalmouth.
It was a sign of things to come, as Julián Alvarez restored parity with arguably an even better finish than Rodrygo’s opener, outmuscling Eduardo Camavinga and smashing a right-footed strike past Thibaut Courtois which clipped in off the post.
Simeone’s side continued to play with confidence after the restart, and Ferland Mendy did well to block Rodrigo De Paul’s effort following a searching cross from Alvarez.
However, it was Real who struck next through Díaz, following a wonderfully-crafted passage of play down the left, also involving Mendy and Vinícius Júnior. The duo linked up superbly to engineer a chance for the Morocco international, who expertly weaved his way into the box and fired a clinical finish past Oblak.
Los Blancos reasserted their control on this contest following the goal, playing with a renewed sense of swagger against an Atlético team suddenly struggling to escape their own half.
There was little in the way of further goalscoring opportunities though, leaving this tie on a knife edge heading into the second leg in eight days' time.
This result denied Atléti from securing a sixth consecutive UCL victory and breaking a club-record winning streak in this competition. They have now won only three of 11 meetings with their neighbours in UEFA competition, but are still firmly in contention to turn this tie around heading into the second leg.
Meanwhile, it is advantage Real, who have now lost only one of their previous 18 European knockout fixtures.