Goals from Frenkie de Jong, Robert Lewandowski, Ansu Fati and Ousmane Dembele temporarily pushed the Blaugrana past Real Madrid at the summit of the Spanish top flight - though their rivals have a game in hand.
There was a lengthy pause late in the second half due to a medical emergency concerning one of the Cadiz supporters, and players were instructed to leave the field as the fan received medical attention. The person is now reported to be in stable condition at a local hospital.
Once the game resumed, Barcelona netted their third and fourth goals.
It was a satisfying result for Xavi and his players after he rotated his line-up with the Champions League back in full swing.
Pedri, Ousmane Dembele and Lewandowski didn't start but were brought into the action just before the hour mark with the scoreline at 1-0 through De Jong's first goal this term - a welcome finish after a summer marred by transfer rumours and contract haggling.
The lead was soon doubled as Lewandowski added the simplest finishing touch to a move that saw the ball roll loose in the six-yard box.
Fati and Dembele rounded out the convincing performance with late goals to take Barcelona's goal difference to 14 through just five games.