Abde Ezzalzouli opened the scoring for Betis, but Porto responded through Gabri Veiga and Samu Aghehowa. Cucho Hernández then equalised before captain Isco converted a late penalty to secure victory.
Ezzalzouli breaks the deadlock
Betis created several promising opportunities in the first half but were unable to find a breakthrough before the interval.
The hosts eventually took the lead in the 47th minute when Ezzalzouli curled a superb right-footed finish into the far top corner.
Porto responded in the 54th minute as Veiga's free-kick from distance found its way past goalkeeper Álvaro Valles.
Porto move ahead before Betis respond
Samu Aghehowa put Porto in front in the 61st minute, striking from inside the area shortly after coming off the bench.
Betis refused to surrender. Cucho Hernández equalised in the 74th minute after receiving a pass from Antony, shifting the momentum back towards the home side.
Isco seals the victory
Betis completed the turnaround in the 84th minute when Isco calmly converted a penalty awarded following a VAR review of a challenge on Ángel Ortiz.
Porto pushed for another equaliser late in the game, but Valles made an important save to preserve Betis' lead.
The result gave Betis six points from their opening two matches in the competition, while Porto were left searching for their first points.