The Argentine forward had a quiet World Cup in South Africa in June and July but looked more comfortable back among his club mates at the Nou Camp.
Messi grabbed two well-taken first-half goals after Sevilla's Abdoulay Konko had put the ball in his own net early on, and rounded off the night with a third at the end.
"We've won another important title after turning round what was a difficult (first leg) result. We now have the first trophy of the season," Messi told Spanish television.
"I treat football as something you have to enjoy and try to do that to the best of my abilities here and with my national team," he replied when asked about criticism he has received in Argentina.
Having lost the first leg 3-1 in Seville last week with a second-string side, Barca fielded an almost full-strength team to win La Liga's traditional curtain raiser for a record ninth time.
Barca coach Pep Guardiola refused to speak about the future of striker Zlatan Ibrahimovic before the match and gave little away as he left the Swede on the bench in favour of Bojan Krkic.
It only took the hosts 13 minutes to open the scoring when Pedro squirmed his way into the area and crossed low for Konko to bundle the ball into his own net.
SUPERB PASS
Xavi's superb 24th-minute pass then put Messi through on goal and the World Player of the Year doubled the lead.
Dani Alves tore down the right and fed Messi, who scored from a tight angle at the near post just before halftime, and Sevilla appeared to switch their attentions to Tuesday's Champions League playoff from then on.
Sevilla slumped to a 1-0 defeat at Portugal's Braga last week.
During the second period the home crowd's chants for favourite Andres Iniesta to be given a run out were answered and Spain's match-winner in the 1-0 World Cup final win over Netherlands was given a rousing reception when he came on.
Iniesta was quickly followed by new 40 million euros signing from Valencia David Villa, who was keen to impress on his debut and almost opened his account with a fierce shot parried by Andres Palop.
Adriano Correia was also given his debut but Ibrahimovic remained unused on the bench and it was Iniesta who laid on the ball for Messi to crash home the fourth.
