The Argentine attacker came off the bench to score a fine goal as the Catalans warmed up in style for the Champions League clash on Wednesday
Lightning doesn't strike thrice. After throwing away a two-goal lead in each of their last two league games against Deportivo La Coruna, Barcelona went on to score all four themselves this time. And Lionel Messi was back with bang.
There were big cheers as the second half started, with Barca already three up through Rafinha (twice) and Luis Suarez (subsequently substituted as a precaution), as Messi began to warm up on the sidelines at Camp Nou.
The Argentine attacker, out with an adductor strain since September 21, came on 10 minutes later and wasted little time as he rifled a fine finish into the net following a Neymar pass shortly afterwards.
Over in Manchester, Pep Guardiola was otherwise occupied. The Catalan coach was busy watching his side in a 1-1 draw at home to Everton. It was City's third successive match without a win, although two penalty misses told a story. In the end, Nolito scored to earn a point for the Premier League leaders. But Barca in this form will be a different proposition altogether.
Last year, Guardiola travelled to Camp Nou to watch Barca in action against City, applauding alongside his father in the stands and covering his face in amazement in a Messi masterclass in which the Argentine nutmegged James Milner.
There were moments of brilliance again from the five-time Ballon d'Or winner in this one and Pep will no doubt watch the tape before Wednesday's meeting between the two teams at Camp Nou. Not that there is much he doesn't know about his former forward anyway.
As well as the Argentine's comeback from injury, Barca were boosted by Rafinha's emergence (the Brazilian international now has four goals from as many starts in La Liga this term) and the return to form of Suarez - although the Catalans will be sweating on his condition after he sat out the second half.
One other small negative was Paco Alcacer's continued strife in front of goal. The Spain striker, who signed from Valencia in the summer, played the second period and got into some excellent positions, but saw three chances squandered in the latter stages and even Luis Enrique looked stunned as the last of those went the wrong side of the post.
Alcacer's moment will come, but this was an emphatic response from Barcelona after their 4-3 loss to Celta Vigo prior to the international break and, on this form, the Catalans look ready to face City on Wednesday.
With Messi back, everything is different.