The victory was Barcelona's sixth consecutive league win, keeping them three points clear of Real Madrid. The result also marked Flick's seventh straight competitive victory to begin the campaign.
• Barcelona: João Cancelo 8', Raphinha 25' (pen), 42', 67' (pen), Asier Villalibre 36' (OG), Gabriel Jesus 79', Lamine Yamal 89'
• Racing Santander: Maguette Gueye 30', Yassir Zabiri 65'
Barcelona started at a furious pace and took the lead after eight minutes. João Cancelo collected a pass from Lamine Yamal before cutting inside and producing a superb long-range finish that went in off the underside of the crossbar.
The hosts doubled their advantage in the 25th minute when Raphinha converted a penalty after being brought down by Racing defender Pedro Felipe. The Brazilian made no mistake from the spot.
Racing responded five minutes later. Maguette Gueye showed excellent composure to get beyond his marker before lifting the ball over Joan García and reducing the deficit to 2-1.
Barcelona quickly restored their two-goal advantage. Cancelo's long-range effort in the 36th minute took a decisive deflection off Asier Villalibre, with the goal officially recorded as an own goal.
Raphinha then struck again in the 42nd minute, finishing another Barcelona attack to complete his first-half brace and send the champions into the interval with a 4-1 lead.
Racing briefly threatened another comeback after the restart when Yassir Zabiri capitalised on a defensive error to make it 4-2 in the 65th minute.
But Barcelona immediately responded. Raphinha completed his hat-trick from the penalty spot in the 67th minute, after another foul on Karim Adeyemi, restoring the three-goal cushion.
Gabriel Jesus added Barcelona's sixth in the 79th minute before Lamine Yamal completed the rout late in the match, making amends for his earlier penalty miss.
The result further underlined Barcelona's extraordinary attacking form. The Catalan club have now scored 33 goals in their opening seven matches in all competitions, while Wednesday's victory gave them their first-ever run of seven consecutive wins to start a season.
Raphinha's hat-trick was the standout individual performance, but Barcelona's attacking threat came from several areas, with Cancelo producing two spectacular efforts and Yamal, Gabriel Jesus and the Brazilian winger all contributing to another emphatic victory.
Barcelona will now turn their attention to their next LaLiga fixture away to Sevilla on Saturday, while Racing Santander will look to recover from the heavy defeat.