Dani Olmo celebrated a "dream debut" on his return to Barcelona as he scored the winning goal in Tuesday's 2-1 comeback win against Rayo Vallecano in LaLiga.

Olmo, 26, missed Barça's first two games of the season as the Catalan side were unable to register him because they remained in excess of their league-imposed spending limit, but his signing was finally processed this week and he made an instant impact in Vallecas.

The Spain international came off the bench at half-time and struck the decisive goal in the 82nd minute as Barça made it three wins from three to start of the season after Pedri had earlier cancelled out Unai López's ninth minute opener.

"I am really happy, really happy with the game and with the win," Olmo told ESPN. "It was a dream debut for me."

Olmo had been made to wait to make his competitive debut after signing in a 55 million deal from RB Leipzig earlier this summer following his exploits for Spain as La Roja won the European Championship.

However, the versatile forward, who came through Barça's academy before leaving for Dinamo Zagreb as a 16-year-old, said he always trusted the club would resolve the financial problems holding up his registration.

"It was a dream, of course, to come back," Olmo added. "I had no doubt when Barcelona knocked on my door. So I'm really happy to be here.

"I was confident the club [would sort out the registration]. I was ready, physically preparing for when I had the chance to start playing. Today I could make it, so I'm really, really happy how it went, how it finished and how it was really important for the team."

Barça coach Hansi Flick was also delighted with Olmo's performance after bringing him on for Ferran Torres at the break with his side trailing 1-0.

"He was waiting a long time to score a goal for Barça," Flick said in a news conference. "When he came on you saw we had more control with the ball. It was really good.

"For him, he brings that, the ball possession is really safe and also in front of the goal he knows how to score goals. For a midfield player it's not normal, but he's really good in this.

"I think the start of the second half was good for us and was the reason he was on the pitch. He's doing great, also without the ball, we are nearer the ball and pressing the opponent very good. He made the difference in the second half."

Olmo's winning goal ensured Barça became the only team in LaLiga to start the season with three straight wins -- a feat they have not achieved since the 2018-19 campaign under Ernesto Valverde.

Flick, though, is not getting carried away after wins against Valencia, Athletic Club and Rayo, insisting his thoughts are firmly fixed on the weekend's game at home Real Valladolid.

"Now we have nine points end everything is good, but it's not like this," Flick said. "We will analyse [the game] and on Saturday we have our next match and we have to play much better than in the first half.

"We defended good, but not perfect in the first half. At half-time I said to the team with 80% it's not possible to win here in this atmosphere with Rayo playing well, many long balls with fast players. It's not easy to defend this. We have to put more pressure on the ball and we did better in the second half."

Barça's win was tainted by a late injury to Marc Bernal, with sources telling ESPN the club fear the 17-year-old has suffered an anterior cruciate ligament injury that could rule him out for the majority of the campaign.

"It's a sad victory because Marc is injured and it looks not so good," Flick said. "We have to wait until tomorrow to see how heavy it is. When you see the dressing room nobody is happy. He made a fantastic match -- 17-years-old and such a performance. It hurts."