Lionel Messi scored a hat-trick to help see off Espanyol in the Catalan derby and take Barcelona top of La Liga.
Messi collected Ivan Rakitic's pass before curling in the opening goal and added a second from close range following Jordi Alba's pull-back.
The Argentina forward completed his 38th Barcelona hat-trick when he finished off from another Alba cross.
Gerard Pique headed in from a corner before Luis Suarez converted from debutant Ousmane Dembele's low pass.
Dembele, the world's second most expensive footballer who joined from Borussia Dortmund for a fee that could rise to £135.5m, came on as a second-half substitute.
Barcelona maintained their 100% record and are yet to concede a goal, while La Liga champions Real Madrid are sixth after a 1-1 home draw against Levante earlier on Saturday.
Messi opened the scoring in the 26th minute, although he was lucky to do so as he looked offside when he collected Rakitic's pass, before jinking inside David Lopez's challenge and curling the ball into the net.
The hosts' lead was doubled nine minutes later when Messi slid in from close range after Alba's pull-back before the five-time world player of the year made it 3-0 after fine link-up play involving Luis Suarez and Alba.
Barcelona dominated possession with 77% of the ball and had further first-half chances but Rakitic was twice denied by goalkeeper Pau Lopez and Suarez shot over the bar.
Espanyol, managed by former Watford boss Quique Sanchez Flores, had chances but Pablo Piatti's shot from 25 yards hit the post and he also shot wide after an Alba error.
Suarez twice missed opportunities in the second half and ex-Tottenham midfielder Paulinho, a second-half substitute, nearly scored on his home Barcelona debut but slid an attempt just wide.
Espanyol substitute Didac Vila forced home goalkeeper Marc-Andre ter Stegen into a good save before Pique scored a fourth, heading in from Rakitic's corner.
After selling Neymar to Paris St-Germain for £200m, Barcelona bought Dembele for an initial £96.8m and he made an impact on his debut, producing the pass for Suarez to add the fifth goal late on.