Despite having not beaten their opponents in the two league matches, Porto were the favourites with the bookmakers to triumph at the Estadio Nacional.
However, they found themselves behind in just the 12th minute as goalkeeper Helton came racing off his line. He was beaten to the ball by Braga attacker Rui Fonte, who lifted over the stranded Brazilian, before he rolled into an empty net.
Helton was then involved in the goal that saw his side's deficit widen in the 58th minute. It was his pass that Ivan Marcano failed to control and Josue pounced to bend the ball inside the far corner.
The response from Porto was positive, though, and within three minutes they had pulled a goal back when Yacine Brahimi's low shot was palmed out by Braga goalkeeper Marafona, only for Andre Silva to turn in the loose ball.
Then, in the first minute of stoppage time, Silva acrobatically volleyed in at the back post to send the clash into extra time and subsequently a penalty shootout.