Franziska Kett kept the home side in the tie with her goal in front of 31,000 fans at the Allianz Arena after 69 minutes. But just ten minutes later, the German international was shown a straight red card for pulling Salma Paralluelo by the hair.
Bayern coach José Barcala was also shown red by referee Ivana Martinčić for his protests, which were futile because a VAR check confirmed Kett’s foul.
Earlier, former Wolfsburg player Ewa Pajor (8') had put Barca, who are aiming for their sixth consecutive final, into the lead.
"A tricky situation. She definitely didn't do it on purpose," explained teammate Klara Buhl about the decisive moment on Disney+.
"She wanted to pull the shirt and would have deserved a yellow card for that, no question. But the hair just got in the way."
Heading into their biggest match of the season so far, Bayern were determined to put the humiliation from October behind them.
"You have to believe in it," said national team player Bühl, who returned to the starting lineup for the first time in over two months after recovering from a calf injury: "Everyone has to show that belief."
Barcelona strikes early
Still, the Munich side's respect for their opponents was obvious. When Barcelona had the ball, Bayern defended deep in their own half and looked to hit on the counter.
That worked from time to time, especially through Bühl. But while Pernille Harder (7') missed the first good chance of the match, Bayern’s supporters must have feared the worst when Pajor scored with the visitor's first shot on target in the eighth minute.
But that was about all Barca managed in the first half. Instead, Bayern grew in confidence with Uli Hoeneß and club boss Jan-Christian Dreesen in attendance, and started to take more risks. Just before halftime, Kett (42') had the best chance for Bayern, but was denied by goalkeeper Cata Coll.
The visitors began the second half on the front foot and came very close to doubling the lead. Esmee Brugts (49') hit the post, and defender Vanessa Gilles (60') cleared off the line for Bayern.
Kett preserved Bayern’s hopes of making the final for the first time when she equalised after a well-worked team move in the 69th minute, as Harder provided the assist.
Bayern held on after Kett’s sending off to leave the tie finely poised before the second leg in the Catalonian capital on 3 May, where Barcelona will bid to reach the final for the sixth successive time.
