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.
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.
