Marc-Andre ter Stegen saved Juanmi's and William Carvalho's poorly-struck spot kicks to give Barcelona a 4-2 penalty shoot-out win over Betis after the teams had finished level at 2-2 following extra time in their Spanish Super Cup semi-final in Saudi Arabia on Thursday.
Barca set up a dream showpiece clash on Sunday with Real Madrid, who had also beaten Valencia on penalties earlier in the week.
Robert Lewandowski gave Barca the lead with a close-range strike late in the first half but Betis came back into the game and deservedly equalised through Nabil Fekir, whose strike extended the match into extra time.
Ansu Fati put Barcelona back in front, finishing off a stunning move from just inside the area, but Betis fought back again and equalised thanks to a brilliant heel-kick from just inside the box by substitute Loren Moron.