The Argentina star swept in a clever free-kick midway through the second half before Philippe Coutinho netted a fine second, with Messi doubling his tally late on to secure all three points for Ernesto Valverde's side.
Alaves did little to trouble Barca's goal even after going behind, but it was far from a convincing display from the hosts, who handed league debuts to Arthur and Arturo Vidal in the second half.
Barca looked laboured despite all their possession in the first half, with creativity at a premium in Coutinho's absence, although captain Messi hit the bar with a free-kick and Ousmane Dembele fired straight at Fernando Pacheco when through one-on-one.
Coutinho was introduced at half-time for full-back Nelson Semedo, but there was little to get the 52,356 fans inside Camp Nou out of their seats until the 64th minute, when Messi sent a free-kick under the wall and into the net.
The Argentina star struck the woodwork again despite nearly slipping over in the build-up, before Luis Suarez – making his 200th appearance for the club – was denied by Pacheco when capitalising on a defensive slip.
Barca secured an opening-day win for the 10th time in succession eight minutes from time, though, when Coutinho rifled home from just inside the area, before Messi brought down Suarez's pass and slotted home with the last kick.
Lionel Messi scored Barcelona's 6000th goal in LaLiga as the champions sealed a 3-0 win over Deportivo Alaves on Saturday.
The Argentina star swept in a clever free-kick midway through the second half before Philippe Coutinho netted a fine second, with Messi doubling his tally late on to secure all three points for Ernesto Valverde's side.
Alaves did little to trouble Barca's goal even after going behind, but it was far from a convincing display from the hosts, who handed league debuts to Arthur and Arturo Vidal in the second half.
What does it mean: Valverde's men still in pre-season mode
Barca looked laboured despite all their possession in the first half, with creativity at a premium in Coutinho's absence, although captain Messi hit the bar with a free-kick and Ousmane Dembele fired straight at Fernando Pacheco when through one-on-one.
Coutinho was introduced at half-time for full-back Nelson Semedo, but there was little to get the 52,356 fans inside Camp Nou out of their seats until the 64th minute, when Messi sent a free-kick under the wall and into the net.
The Argentina star struck the woodwork again despite nearly slipping over in the build-up, before Luis Suarez – making his 200th appearance for the club – was denied by Pacheco when capitalising on a defensive slip.
Barca secured an opening-day win for the 10th time in succession eight minutes from time, though, when Coutinho rifled home from just inside the area, before Messi brought down Suarez's pass and slotted home with the last kick.
Boot up the backside: Dembele frustrates again
Dembele looked ready for an explosive start to the season when he blasted in the winner in the Supercopa de Espana, but this was another forgettable outing at Camp Nou for the forward.
He squandered two decent first-half chances with poor finishes after failing to pick out Messi in a two-on-one situation, and his runs in the final third too often ended in possession being gifted to Alaves.
