The 21-year-old, who completed a high-profile move to Spain at the end of May, came on at half-time at the Nou Camp and set up Cesc Fabregas to score his second of the night before shaving the crossbar with a fierce effort of his own late on.
World Player of the Year Lionel Messi set Barca on their way with a goal in the eighth minute and was on the pitch with Neymar for the first time for just over 15 minutes at the start of the second half before the Argentina forward was substituted.
Santos defender Leo netted an own goal in the 12th minute before Alexis Sanchez made it 3-0 to the home side 10 minutes later and Pedro added another in the 28th.
Spain midfielder Fabregas looked sharp after he came on at half-time and quickly made it 6-0 with a well-taken double before smashing a free-kick against a post and Adriano and B team teenager Jean Marie Dongou completed the rout.
Barca begin the defence of their La Liga title, when they will be chasing a fifth triumph in six seasons, at home to Levante in just over two weeks.