BBC Sport - Anthony Gordon scored his first Champions League goal for Barcelona as the Spanish side came from behind to beat Galatasaray in Istanbul.
Barcelona sought to extinguish the febrile atmosphere early on by controlling possession, but fell behind after Galatasaray's first proper attack.
Seconds after Gordon's claims for a penalty were ignored, Rafael Leao charged down the left wing and cut the ball back into the path of Aleksey Batrakov, who found the bottom corner via a deflection off Joao Cancelo.
Galatasaray thought they had doubled their lead six minutes later when Baris Alper Yilmaz diverted Victor Osimhen's header past Joan Garcia, but the goal was disallowed for a marginal offside after a video assistant referee (VAR) check.
Barcelona steadied themselves and silenced the frenzied home support two minutes before the break, as Dani Olmo deflected the ball into the path of Joao Cancelo who curled a strike into the corner past Turkish goalkeeper Ugurcan Cakir.
Any vulnerability the visitors showed in the first half quickly evaporated in the second as Hansi Flick's side scored twice in quick succession.
Fermin Lopez headed in from a Lamine Yamal cross in the 50th minute, and three minutes later a supreme piece of close control from the latter set up Gordon to fire in his first Champions League goal for Barcelona three days after netting for the club for the first time.
Fellow summer signing Karim Adeyemi replaced Gordon and arrowed in Barcelona's fourth goal from the left side of the penalty area after Gabriel Jesus touched a Lamine Yamal cross into his path.
Barcelona have scored 84 goals in 28 Champions League matches under Flick, giving them the highest goals-per-game ratio (3) in the competition for any club with 20 or more games under a specific manager since 1992-93.
Barcelona have six points after thrashing Feyenoord 5-1 in their league phase opener, and will now travel to France to face Paris St-Germain on Tuesday, October 20.
After losing 3-1 to Sporting CP last month, Turkish Super Lig leaders Galatasaray will look to claim a first win of the campaign when they face Lille on Wednesday, October 21.