Eibar started the game brightly and had the first chance in the third minute when David Juncà caught the Barcelona defence out, setting Sergi Enrich up with a through ball. However, Marc-André ter Stegen did well to block his shot at goal.
The complexion of the game changed in the 20th minute, when Nélson Semedo went down in the box under a challenge from Gálvez and won his side a penalty.
As usual, Messi made no mistake dispatching the spot-kick, placing his shot perfectly in the top left corner.
In the 38th minute, Paulinho got on the end of a Denis Suárez corner and fired a powerful header into the net, sending the hosts into the break 2-0 up.
It didn’t take long for Barcelona to pick up where they left off after the break. A Messi shot was saved by Marko Dmitrovic, but fell straight into the path of Suárez — who slotted it home.
Eibar refused to lie down and were finally rewarded in the 57th minute when Juncà found Enrich with a cross and the striker got the decisive touch to steer the ball into the net.
It only took two minutes for Barcelona to respond as Messi rolled an inch-perfect left-footed shot into the bottom corner of the net.
The Argentine completed his hat-trick in the 62nd minute as Barcelona hit Eibar on the break and Paulinho set the star man up for his third goal.
Twenty-five minutes later Messi rounded off a stunning show by playing a one-two off Aleix Vidal and stroking the ball into the back of the net without taking a touch to control it.
The win will give Barcelona confidence that they can cope during Ousmane Dembélé’s lengthy injury layoff and will put pressure on defending champions Real Madrid ahead of their Wednesday game against Real Betis.