Lamine Yamal returned from injury to help Barcelona beat Real Sociedad 2-1 on Sunday and move top of LaLiga by one point.
After Real Madrid were thrashed 5-2 by rivals Atletico Madrid in a derby on Saturday, Hansi Flick's side had the chance to claim pole position above Xabi Alonso's side.
Alvaro Odriozola gave Real Sociedad the lead against the run of play in the first half, but Jules Kounde headed the Spanish champions level.
Yamal, who missed the last four games with a groin injury, created the winner for Robert Lewandowski just moments after coming on as a second-half substitute.
"I'm very happy for (Yamal), very pleased that he's back on the pitch because we're going to need him," Kounde told Movistar.
Barcelona held the game at the Olympic Stadium, where they have played for the last two seasons, after the city council refused them a permit to reopen their Camp Nou home earlier in the week.
Flick handed 17-year-old attacking midfielder Dro Fernandez his debut, also starting Roony Bardghji on the right wing and bringing in veteran Wojciech Szczesny for injured goalkeeper Joan Garcia.
Barcelona dominated the ball in the first half but found it hard to beat Real Sociedad goalkeeper Alex Remiro.
The Spain international made a fine save to deny Marcus Rashford in the early stages.
On loan from Manchester United, Rashford is finding his footing at Barca and played a superb through ball for Lewandowski, who fired across the face of goal from a tight angle.
Real Sociedad hit Barca with a sharp counter-attack to open the scoring after 31 minutes.
Former Real Madrid defender Odriozola applied the finishing touch to Ander Barrenetxea's cross.
Barcelona stepped up a gear and found Remiro in their way again, with the goalkeeper superbly palming away a Kounde cross which was deflected towards his goal.
Remiro also tipped a Bardghji effort away for a corner, which led to Barcelona's equaliser.
Rashford, who provided an assist from a corner against Real Oviedo in midweek, whipped it to the near post, where Kounde powered home a header.
YAMAL RETURN
Flick replaced Dro with Dani Olmo at halftime and also brought on Yamal before the hour mark, after the teenager recovered from his groin issue.
Voted the second-best player in the world at the Ballon d'Or gala on Monday, Yamal made an instant impact.
The 18-year-old burst into the box and crossed for Lewandowski to head home off the post, just over a minute after his introduction.
Szczesny made a good save from Oyarzabal as La Real gave Barcelona a couple of scares, while Remiro denied Rashford and Olmo with two more good saves.
The game grew increasingly chaotic and both sides hit the crossbar in quick succession.
Kounde, daydreaming in midfield, was robbed and Real Sociedad worked the ball to Takefusa Kubo, who crashed a shot against the woodwork.
Then Barcelona broke away and Ferran Torres teed up Lewandowski, who battered the crossbar when well placed to put the game to bed, but the hosts were not punished.
"It was a difficult game, I didn't like our last 25 minutes, we suffered too much," added Kounde.
"The first 70 minutes I think were quite good, we could have scored more than two... but I didn't like how it ended."
Barcelona host Paris Saint-Germain in the Champions League on Wednesday, also at the Olympic stadium.
Real Sociedad have had a tough start to the season, sitting 17th, but have been improving and will take heart from the pressure they put Barca under.
"Despite the defeat, I'm proud of the team's work," said Odriozola. "It's been a tough start and today we showed up."