Real Madrid substitute Marco Asensio scored a second-half winner on Wednesday to end Bayern Munich's unbeaten record at home this season and give his side a 2-1 win in the first leg of their Champions League semifinal.

Joshua Kimmich had put the home side in front, but Marcelo equalized before the interval against the run of play. Asensio then came on after the break and Lukas Vazquez set up the 22-year-old to claim a second away goal for Madrid 12 minutes into the second half.

The result puts the two-time defending champions in a favorable position before the second leg in Madrid next Tuesday, though Zinedine Zidane's side will be wary after conceding three goals at home to Juventus in the previous round.

Bayern had to substitute the injured Arjen Robben and Jerome Boateng in the first half, but the side had plenty of chances to score more goals with Franck Ribery, Thomas Mueller and Robert Lewandowski all missing good opportunities.

Cristiano Ronaldo was held scoreless for the first time in the competition this season. The Portuguese star had an effort ruled out in the second half for using his arm to control the ball.

Bayern, which is chasing a treble in Jupp Heynckes' last season in charge, was hoping to make up for last year's quarterfinal exit to Madrid, and for the Spanish side's 5-0 aggregate win at the same stage in 2014.

Roy Makaay scored the fastest Champions League goal after 10 seconds for Bayern against Madrid in 2007, and Mueller would have rivaled it had he been able to make more of a chance created by Lewandowski.

Rafinha had the first shot on goal in the 19th minute after a cautious start from the visitors, who started with both Gareth Bale and Karim Benzema on the bench.

Madrid started to settle midway through the half before Kimmich struck. James Rodriguez played the right-back through as Bayern created a three-on-two. Perhaps expecting a cross, Navas was surprised when Kimmich let fly to score inside the far corner.

Buoyed by the goal, Bayern's players suddenly found spaces but Ribery wasted a good opportunity to double the lead.

Instead, Marcelo leveled the score shortly before the break. Dani Carvajal headed the ball back into the danger zone, Ronaldo let the ball bounce, and Marcelo let fly with a low shot inside the bottom corner.

Bayern missed more chances before the interval, when Asensio came on for Isco to change the course of the game. After Bayern turned the ball over in midfield, Vazquez and Asensio played a one-two before the substitute coolly dispatched the ball past Sven Ulreich.

Navas pulled off a brilliant save to deny Ribery, who was again blocked by the 'keeper five minutes later. Mueller missed an even better chance minutes after that.

Ronaldo thought he'd scored with around 20 minutes remaining, but the goal was ruled out and his run finally stopped.