Tito Vilanova's debut could not have gone any better, with a sublime victory full of attacking quality, made even better by the goalscoring comeback of Villa.
As Real Madrid stumbled to an early 1-1 draw against Valencia earlier, Vilanova picked up where predecessor Pep Guardiola left off, dominating the beleaguered visitor for large periods to clinch an emphatic home victory.
Carles Puyol's header gave Barca the lead after four minutes, only for Chory Castro to restore parity with an opportunistic finish moments later. But then Messi took over, scoring a pair of poacher's efforts in the 11th and 16th minutes to give the Catalans a lead they would never relinquish.
Pedro added the fourth just before half time, and Barca's perfect beginning to the season was completed by the return of David Villa from injury, who scored the fifth and final goal six minutes from the end.
Vilanova was not the only debutant for Barca, as Jordi Alba, the 14 million euro signing from Valencia, was handed a start at left back. Sociedad’s own new recruit Chory Castro began up front, but fellow summer signings Carlos Vela and Jose Angel had to settle for a place on the bench.
It took the Catalans only four minutes to break the deadlock, though the goal came, for them, in somewhat unconventional fashion. A corner from Xavi was thumped in by the head of Puyol to send the hosts in front.
Sociedad was straight back down the pitch. Asier Illarramendi slipped a clever pass just in front of Dani Alves, putting Castro through, where he had the time to take a touch and bury his finish high into the roof of the net after.
But just as Sociedad was able to hit back after conceding, so too did Barcelona, which regained the lead within two minutes of restarting the match. Messi’s uncharacteristically poor touch spilled a decent cross from Tello, but Pedro worked the rebound back into the Argentine, who wriggled through his markers and slotted home.
Messi’s instincts came to the fore moments later, the forward reacting quickest to a Tello center to drill the Blaugrana into a 3-1 lead, all after 16 minutes. With a two goal cushion, the hosts settled into their typical monopolization of possession, suffocating Sociedad in its own half with large periods of metronomic passing.Barcelona was always in control, and, with four minutes to go until half time, it added a fourth in emphatic and enthralling fashion. Messi, Xavi and Fabregas were all involved in a build-up that split Sociedad in two, with the decisive ball worked to Tello on the left, who centered to Pedroto stroke into the far corner.
Sociedad set up for a damage-limitation exercise in the second half, though Antoine Griezmann snatched at an early opening as he fired wide from a good position.
However, the focus was always at the other end of the pitch, and an outstanding one-touch sequence between Messi and Pedro ended with the former blasting his finish into the side netting when he should have hit the target.
The home fans were in jubilant spirits, which were kicked up a notch by the introduction of Villa for Pedro with a quarter of an hour to go, the Spain striker making his long awaited return from a broken tibia last December. And Villa did not miss a beat, finishing a mazy run from Iniesta with aplomb in the 84th minute to round off a picture-perfect start to the new season for Barcelona.