Dani Olmo celebrated his delayed Barcelona debut with a goal to seal a 2-1 comeback victory at Rayo Vallecano in LaLiga Tuesday.
The Spain playmaker's 82nd-minute strike helped Barca claim their third win from three matches under new coach Hansi Flick at the start of the season.
Barca were unable to register Olmo with LaLiga after signing him from RB Leipzig until earlier in the day and he made an instant impact after being brought on at Rayo's Vallecas stadium.
Unai Lopez sent Rayo ahead against a flat Barca in the first half but Olmo came on at the break and energized the Catalans, who levelled through Pedri Gonzalez before the new arrival struck the winner.
"(I've been waiting to play) since I arrived, looking forward to the first game, the debut, and what better way (to mark it)," Olmo told DAZN.
"I was really looking forward to it, I felt physically ready to play, and it finally happened.
"I am very happy to have made my debut and helped the team."
In the final stages 17-year old defensive midfielder Marc Bernal was taken off after appearing to twist his knee and Flick was worried about the youngster, who has impressed at the start of the season.
"It's a sad victory because Bernal is injured and it looks not so good," said the German coach.
"We have to wait and see how heavy it is.
"We win, it's OK but when you see the dressing room nobody is happy."
Vallecano, celebrating their centenary year, signed former Real Madrid playmaker James Rodriguez earlier in the week and he watched on from the presidential box as the capital club started strongly.
The hosts attacked with intent and got their reward when Jorge De Frutos drove forward on the right and crossed for Lopez, who finished with a low effort at the near post.
Rayo minimized Barca's threat in the first half except for the odd occasion teenage star Lamine Yamal managed to work his magic.
Flick hooked Ferran Torres at half-time and threw on Olmo for his debut, after he had missed the first two league matches waiting for Barca to get their finances in order to complete his registration.
With Olmo entering the fray he took up a central attacking midfield position, with Brazil winger Raphinha restored to the left flank.
The former Barca academy player quickly began to make his mark on proceedings and the Catalans started to generate chances.
Polish veteran Robert Lewandowski should have levelled but could not get a solid touch close to goal on Raphinha's dangerous cross.
Raphinha whistled a free-kick narrowly wide and Olmo smashed a 30-yard drive against the crossbar.
Barca made the pressure count and Pedri levelled on the hour mark after exchanging passes with Raphinha and sweeping home.
Barca thought they had a second 10 minutes later, when Yamal's shot was saved and Lewandowski worked room to tuck the rebound home.
However the goal was controversially disallowed after a Video Assistant Referee referral when the referee deemed Jules Kounde guilty of a foul, when he made light contact with Pep Chavarria's foot in the build-up.
The visitors did not lick their wounds for too long, maintaining the pressure, and Olmo finished with aplomb after Yamal set him up.
"I'm always a player who looks to score, Lamine found me well and I finished well, a good goal, I'm very happy," added Olmo.
Barca played with an energy in the second half which has often been missing late in games in recent years, with the team appearing notably fitter under Flick.
The victory guarantees Barca will top the table after the third round of matches, despite various injury issues affecting important players including Gavi, Frenkie de Jong and Ronald Araujo.
Bernal has started all three of Barca's games this season and the club will hope he does not join the list of long-term absentees.
Champions Real Madrid visit Las Palmas Thursday while Atletico Madrid host Espanyol Wednesday, among other fixtures.
RESULTS
Mallorca 0 Sevilla 0
Vallecano 1 (Lopez 9) Barcelona 2 (Pedri 60, Olmo 82)
Monday
Villarreal 4 (Cardona 26, Barry 60, Jailson 64-og, Parejo 90+10) Celta 3 (Iglesias 12, Mingueza 31, Starfelt 80)