Poland striker Robert Lewandowski's brace earned depleted Barcelona a 2-1 comeback win at Valencia in their opening game of the LaLiga season on Saturday.
Barca were dominated by their hosts early in the match and fell behind when Valencia's Hugo Duro netted a close-range header in the 44th minute.
The visitors hit back quickly, however, scoring either side of halftime through Lewandowski who tapped home Lamine Yamal's cross deep into added time before the break and fired an unstoppable penalty into the top corner after Raphinha was fouled just after the interval.
Thanks to his strikes, the Hansi Flick era began with a gritty win against a tough side at a sold-out Mestalla stadium despite Barcelona missing several key players and featuring three 17-year-olds from the start of the game.
With Ilkay Gundogan, Pedri, Gavi, Ronald Araujo, Frenkie De Jong and Ansu Fati all out with injuries and new signing Dani Olmo yet to be registered with LaLiga due to Barca's breach of Financial Fair Play (FFP) rules, the German manager was forced to be creative in his selection.
Marc Bernal, Lamine Yamal and Pau Cubarsi - all still 17 - were on the starting list in the scorching heat and humidity on the east coast of Spain.
Valencia dominated proceedings early and Rafa Mir was inches from scoring for the locals with two diving headers in the first few minutes, while Cubarsi almost netted two own goals while trying to deflect efforts by Andre Almeida and Diego Lopez.
One minute after Duro gave Valencia the lead, however, Cubarsi made an astonishing goalline clearance to deny Valencia a quick second when Mir had already beaten goalkeeper Marc Andre ter Stegen. That kept Barca in the game, paving the way for Lewandowski's double.
The Pole's first goal was a result of a fine collective effort with Alejandro Balde delivering a long cross from the left touchline to the back post to meet 17-year-old Lamine Yamal, who turned the ball back along the six-yard box with a single touch, leaving Lewandowski with a simple tap-in.
In the second minute of the second half, defender Cristhian Mosquera tripped Raphinha inside the box, gifting a penalty to Barcelona which Lewandowski fired into the top corner.
With Barca in front, the momentum of the game changed completely and the visitors had several chances to extend their lead against a Valencia side who appeared unable to find the spark to fight back.