The visitors got off to a furious start on Wednesday, attacking at will and grabbing an early lead in the latest Clasico between the two titans of Spanish football.
But the hosts recovered and were the better side in the second half in front of 92,000-plus spectators at Barcelona's Camp Nou.
Facing his biggest match since taking charge of the Blancos in late October, Santiago Solari devised a plan that worked to perfection for the opening 20 minutes.
Real Madrid enjoyed free rein against a home squad that looked unsure of themselves from the starting whistle.
The Blancos front three of Lucas Vazquez, the speedy Vinicius Jr. and an in-form Karim Benzema not only put pressure, they neutralized Barcelona midfield playmakers Sergio Busquets, Ivan Rakitic and Arthur.
The visiting midfield trio of Marcos Llorente, Toni Kroos and Luka Modric were free to create.
In the 6th minute, Vinicius directed a pass to the far post that eluded Barça defender Jordi Alba. Benzema controlled the ball and passed to Vazquez waiting in the box and Real Madrid led 1-0.
The pitch remained tilted in the Blancos' favor until the 19th minute, when Brazilian forward Malcom - Barcelona's best player on the night - looked set to equalize before losing the 1v1 battle with Real Madrid keeper Keylor Navas.
A cross from Malcom set up a chance for Gerard Pique in the 27th minute and Rakitic got his head to the Brazilian's free kick five minutes later only to hit the post.
The initiative belonged to the hosts for the rest of the first half, though it was hardly classic Barça football, with efforts marked by plenty of heart but little of the usual technical excellence.
As the first 45 minutes drew to a close, an anxious Leo Messi could be seen sitting on the Barcelona bench fidgeting with a water bottle. The Argentine superstar had been doubtful for the match up until 24 hours before the kick-off at Camp Nou after getting hurt last weekend in a La Liga match.
Barça retained the upper hand after the re-start and the equalizer came in the 58th minute, when Malcom converted the rebound after Luis Suarez hit the post.
The score knotted at 1-1 with 30 minutes left, Solari sent in Casemiro for the injured Llorente and replaced Vinicius with Gareth Bale.
Barcelona coach Ernesto Valverde substituted Arturo Vidal for Rakitic in the 62nd minute, a minute before pulling Philippe Coutinho to make room for Messi.
With fatigue taking hold at both ends of the pitch, it was clear that only a brilliant individual effort would break the deadlock and Bale did his best to deliver, a foray in the 82nd minute that Semedo handled with aplomb.
The 1-1 held up to the final whistle, setting the stage for a potentially epic second leg at the Santiago Bernabeu on February 27.
Barcelona, with 30 Copa del Rey titles to their credit, are hoping to hoist the trophy for a fifth consecutive year.
Real Madrid have won the competition 19 times.
