João Félix scores against his former club to put Barca ahead (1:06)João Félix chips the keeper to put Barcelona on top of his former club Atletico Madrid. (1:06)
After netting in the 28th minute, João Félix stood on the advertising hoardings at the Olympic Stadium, arms aloft in front of the visiting Atlético supporters.
The Portugal forward joined Barça on a season-long loan from Atletico in September and said the celebration related to difficult moments prior to securing the move.
"It was spontaneous," he told Movistar after the game. "At the end of the day, you're in the heat of the game and it was almost [a feeling of] relief for everything I went through in the summer.
"Only those closest to me, my family mainly, know what I went through. This was for them; I felt relieved for them, too."
The build-up to the game had been dominated by a war of words between Félix and some of his former teammates.
He said they would like to play more attacking football and they accused him of being inconsistent, but he attempted to downplay any bad blood.
"I get on well with them," he added. "They know it has nothing to do with them. I have nothing against them. I hope things go well for them, just not against us.
"Every week there is talk about me, for good or for bad. I focus on my job, without looking at what people say or think. I am working to improve and be a better player."
His goal against Atlético -- the only one of the game for either side -- comes just four days after his winner against FC Porto in the Champions League in midweek.
"Once again he made the difference for the team," Barça coach Xavi Hernández said in a news conference after the game.
"He worked hard, won a lot of balls back, was really good positionally and he has a good understanding with [João] Cancelo on that [left] flank.
"I am delighted for him. He's happy and is making the difference in games, which is fantastic for him. It was an intelligent performance because sometimes when you are so motivated can cross a line."
Félix later told ESPN that he hopes Barcelona will sign him permanently.
"That is more a question for the sporting director than me," Xavi said of the chances of a deal happening. "But I am very happy with him. He is working hard, performing well and is a great kid in the dressing room. I am delighted to have him in the team."
Barcelona's Joao Felix celebrates after scoring a goal against Atletico Madrid in LaLiga. Getty Images
Raphinha also hit the post after the break and Lewandowski shot wide after a good solo run, leaving Xavi with the feeling his team should have won by a bigger margin.
"The team was excellent today," Xavi added. "It's a game we should have won by more. I am very satisfied and happy with how we played. It was a complete performance with the exception of the last five minutes.
"Atlético pressed us in the second half, but we have seen our most complete performance of the season. It's a sign that we grow when the big games come around. We have to demand that we always plays like this.
"It has been an important week. We have peace of mind in Champions League after progressing [to the last 16] and have now won against a direct title rival playing really well."
Atlético took a while to get going but finished strongly in Montjuic. Memphis Depay saw a free kick tipped on to the bar by Iñaki Peña, who replaced the injured Marc-André ter Stegen again, and Ángel Correa shot at the goalkeeper late on.
"It was a game of two halves," Atlético coach Diego Simeone said. "In the first half, Barça were better. Despite that, we still had the moment with [Nahuel] Molina and another chance.
"In the second half, the [three substitutions we made at the break] changed the dynamic of the game. I thought we did enough to score.
"Their goalkeeper, above all the save from the Memphis, was amazing. It is a shame that in the spell when we were better, creating four chances, we were not as clinical as they were in the first half."
Atlético slip to fourth with the defeat, but can join Barça four behind Madrid and Girona if they win their game in hand at home to Sevilla later this month.
Barça, meanwhile, host LaLiga's surprise package Girona next Sunday.