BARCELONA, Spain — Lionel Messi scored a hat trick and Ousmane Dembele set up a goal in his debut for Barcelona in a comfortable 5-0 win over crosstown rival Espanyol on Saturday.

Messi struck twice in the first half, and leads the Spanish league with five goals. Gerard Pique headed in a fourth goal.

After going on as a second-half substitute, Dembele didn’t take long to help his team when he passed for Luis Suarez to round off the rout in the 90th.

A third win in as many rounds left Barcelona atop of the standings, with two more points than second-place Sevilla and four more points than defending champion Real Madrid in sixth.

Messi opened the scoring at Camp Nou when he received a pass from Ivan Rakitic in what appeared to be an offside position. With no call coming from the referee, Messi dribbled around a defender and fired home.

He got his second by sliding to redirect Jordi Alba’s pass by goalkeeper Pau Lopez. Messi started the attack but lost the ball, only for it to take two deflections off defenders before falling to Alba in the area.

After Espanyol forward Pablo Piatti hit the post, Messi made it a treble with a left-footed strike to slot in another pass from Alba.

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Dembele went on moments later to a round of applause from his new supporters. Barcelona paid a club-record sum to Borussia Dortmund for the 20-year-old France forward. With add-ons, his transfer could reach 147 million euros (about $173 million).

Dembele showed his speed when he raced down the right side on a quick counterattack and crossed for Suarez to score.

Suarez was making his league debut this season after missing the first two matches with a leg injury.