Los Blancos lost no time putting pressure on Athletic, controlling and rapidly moving to ball in an attempt to find a week spot in the local team's defense.
Real Madrid was close to scoring in the first minute, though Luka Modric's shot from close range, after a great cross by Gareth Bale, flew to the right of the post.
The Rojiblancos began to react at around the quarter-hour mark.
In the 14th minute, a shot from the right side by Athletic's Iñaki Williams flew to the left of the post, while a long-distance shot by Markel Susaeta just one minute later flew just over the upper-right corner.
In the 22nd minute, Athletic's Yuri Berchiche found an opportunity with a long-distance shot from the left, though the ball was blocked by keeper Thibaut Courtois, only to bounce back to Berchiche, whose second shot flew right into the goalie's hands.
Real Madrid was close to scoring in the 29th minute, though Marco Asensio's shot from the left was met with a great save by Athletics's Unai Simon.
The Rojiblancos scored just two minutes later, as Susaeta swerved his way into Real Madrid's box, passing the ball to Iker Muniain, who tapped it in from close range.
After the break, Real Madrid's Casemiro replaced Dani Ceballos, giving the team more speed, while Athletic lost some of their stamina as Muniain was replaced by Ander Capa.
The tie came in the 63rd minute, just after Isco replaced Modric.
Isco connected a brilliant cross by Bale from the right, placing the ball neatly into the left corner of the goal with a close-range header.
Athletic's Simon made another great save in the 68th minute, blocking a close-range shot by Asensio, and providing the Rojiblancos with the needed confidence to treat Real Madrid as equals.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)