Barcelona moved seven points clear of Real Madrid after continuing their 100 percent record in with a 2-1 win at Getafe.
Barca were however made to struggle and they had to come from behind.
But they could be without record signing Ousmane Dembele for a number of weeks after the French winger hobbled off in the first half with a hamstring injury.
“Fortunately, it was an important test for us. We managed to turn the game around and that power of reaction the team had means a lot,” said Barca boss Ernesto Valverde.
Paulinho’s 40 million-euro signing from Guangzhou Evergrande was just one of a number of much-criticised moves by the Barca board following the departure of Neymar to Paris Saint-Germain.
But the Brazilian international showed his worth by smashing home Lionel Messi’s through ball to score the winner.
“I’m very happy to score the goal. It was the winner which was the most important thing,” Paulinho told Barca TV.
“It was a difficult game because Getafe have players with quality and we conceded the first goal but we were calm, had patience and went looking for the result.”
Barca had barely replaced Dembele with Gerard Deulofeu before they fell behind six minutes before half-time.
Sergi Roberto’s headed clearance fell invitingly for Gaku Shibasaki, who made his name with two goals against Real Madrid in last year’s Club World Cup final for Kashima Antlers, to thunder an unstoppable dipping volley beyond Marc-Andre ter Stegen.
Valverde made another change at the start of the second period as Denis Suarez replaced Iniesta.
And it was the substitute who inspired Barca’s revival as he collected Roberto’s cut-back from the right wing before bending the ball high past Vicente Guaita into the top corner.
Paulinho completed the comeback when he burst onto Messi’s through ball and smashed across the despairing Guaita into the far corner.