He missed a back-pass from Corentin Tolisso, leaving Benzema to tap into an empty net.
This season's tournament has seen Ronaldo, the all-time leading scorer in the competition with 120 goals, become the first player to score in 11 successive Champions League games. "We suffered against a great team, but at the end of the day, we did it again". The referee did a good job, we didn't lose because of him.
Real coach Zinedine Zidane has had to face nearly weekly questions from the media about Benzema's form and where it left his future at the club, and the forward came in for renewed scrutiny after a poor display last Saturday against Leganes.
Bayern's sports director Hasan Salihamidzic poured praise on Heynckes. "We really wanted to reach the final and we gave our best and then this unnecessary mistake happened to me", Ulreich wrote on Instagram.
The Columbian is now on a two year loan deal at Bayern from Madrid and was in a unique situation playing against his parent club.
Zidane, however, said he and the rest of the Madrid squad had kept their faith in the striker despite his struggles.
"I do not feel the emotion "yes, now it's over", I'm disappointed with the result, especially for the players".
Still, Bayern could count themselves unlucky not to have been awarded a penalty and Real left-back Marcelo admitted as much afterwards.
With the scores level just after the break in Tuesday's second-leg, Ulreich's blunder gifted Karim Benzema his second goal and Real the lead. "If I tell you that the ball has not touched my hand, I'm a liar", Marcelo said afterwards.
Bayern coach Jupp Heynckes was not asked about the incident in the post-game news conference and nor was Zidane, though Bayern's injured defender Jerome Boateng expressed his disbelief at the decision on social media.
And Real captain Sergio Ramos believes the pedigree of his team, who are chasing an unprecedented third Champions League trophy in a row, makes them favourites whoever they face. Not only is this the most by an English side during a single European Cup campaign, but it's one short of Real Madrid's overall record (41) set in 2013/14.
Bayern had also been wasteful in the 2-1 first-leg defeat by Real in the first leg at the Allianz Arena. "If you have the chances we had, you have to get to the final".
In an nearly carbon copy of the second leg against Juventus in the quarter-finals, Real were left hanging on at the Santiago Bernabeu in added time. "But Navas was outstanding". Real didn't play their best game but made fewer grave mistakes. But it wasn't to be, partly we have ourselves to blame, partly we were out of luck. "Obviously we have to ask what we are doing wrong in these semi-finals".