JOIN USAn awful back pass in the 39th minute by Colombia midfielder Fredy Guarin was intercepted by Messi and the Argentina forward slotted the ball in to the net after showing masterful balance to sidestep goalkeeper Helton.
Europa League winners Porto fell further behind after 88 minutes when Messi chipped a pass and substitute Cesc Fabregas controlled the ball with his chest before firing in.
Rolando was sent off for a second bookable offence in the 86th minute and Porto team-mate Guarin received a straight red card four minutes later for lunging at Javier Mascherano.
Barca, who will make a delayed start to their domestic league season when they meet Villarreal on Monday, have now collected two major trophies in 10 days following their Spanish Super Cup triumph over arch-rivals Real Madrid.
“It was tough to beat Porto, they are a great team,” captain Xavi told Spanish television. “The pitch was not in good condition, they are a very physical side and pressed us high up.
“We maybe weren't as superior as in other matches but ... it's another European title that fills us with excitement. This team is making history and we believe we can still win more trophies.”
Messi, named on Thursday as the inaugural winner of UEFA's Best Player in Europe award, continued where he left off last season -- a campaign that yielded 53 goals.