Barça started in fine style at the Camp Nou and they had a reward as early as the fourth minute. A Leo Messi pass set Nelson Semedo free down the right-hand side before the right-back crossed for Antoine Griezmann to slot home.
The Frenchman almost had a second before 10 minutes had been played, but after consultation with VAR, the goal was ruled out. Jordi Alba fizzed one across goal just after the quarter hour, as Barça ramped up the pressure on their visitors.
Leganés responded soon after with Aitor getting their first shot on target, but there was no let up from the hosts with Arturo Vidal, Gerard Piqué and Griezmann going close. On 28, a wonderfully flighted corner from Messi found Clément Lenglet and the Frenchman’s glancing header nestled in the back of the net, putting Barça firmly in control.
Sporadic attacks from Lega were quickly thwarted as the pattern continued until half-time, the blaugranes knocking the ball around with pace and accuracy.
Try as the visitors might, with only one striker up front they found it difficult to manufacture any chances of note. They were soon punished as Messi was given the freedom of Camp Nou to put Barça 3-0 up just before the hour mark, albeit via a deflection.
Daylight between the sides allowed Quique Setién to bring on Ivan Rakitic, Junior Firpo and Arthur Melo, and it was the latter who made it four on 77, after both Ansu Fati and Messi had seen their shots blocked.
With two to play, Messi rounded Ivan Cuellar and smashed the ball into the roof of the net to complete the rout.