The midfielder scored inside the opening minute at the Metropolitano, setting Atletico Madrid on their way to their first win in the league phase. The result was particularly emotional because Koke had been ruled out after his mother passed away earlier on Tuesday.
Barrios had already decided how he would celebrate if he found the net. His goal was followed by a gesture in tribute to the absent captain, whose number six shirt was the inspiration for the celebration.
Speaking after the match, Barrios explained the significance of the result.
“First of all, as well as for the team, this was very important for Koke and his whole family. It is a very difficult day for them. This victory is for them.”
The 22-year-old said the dedication came naturally after the news reached the dressing room.
“It was very difficult news for all of us, and I said that if I scored, I would do that. It just came naturally to me.”
His early strike also helped Atlético establish control of a match in which Manchester United had opportunities to respond. Barrios acknowledged that the visitors created chances, but felt his side had delivered a disciplined performance.
“The goal so early helped us manage the match afterwards. We are very happy with the victory.”
He added: “It was a good performance from the team, although they also created chances against us. We played a very serious game and secured our first victory.”
Atlético appeared to have extended their lead before the interval when Johnny Cardoso found the net, but the goal was disallowed following a review for a handball involving Marcos Llorente earlier in the move.
Barrios admitted he had not seen the incident again and could not offer a definitive view.
“I haven't seen it again. Marcos said he wasn't sure about it. I haven't seen it.”
Atlético eventually confirmed the result through Ademola Lookman, who scored in the second half after Leny Yoro had been sent off for Manchester United.
The victory provided an important European boost for Diego Simeone's side, but the occasion remained centred on their captain. Barrios's opening goal and subsequent dedication ensured that Koke and his family were remembered throughout a night that combined a significant result with a personal loss.