Cape Town - Barcelona overturned a first leg defeat to beat Levante in the Copa del Rey on Thursday but could yet be thrown out of the competition after being accused of fielding an ineligible player.
Barca won 3-0 at the Camp Nou, with Lionel Messi setting up two Ousmane Dembele goals and then scoring himself to seal a 4-2 victory on aggregate.
Their place in the quarter-finals, however, is under threat after Levante president Francisco Javier Catalan confirmed shortly before kick-off that the club would lodge a complaint to the Spanish Football Federation on Friday.
Levante claim Barcelona defender Juan Brandariz 'Chumi' played illegally in the first leg as he should have been serving a suspension.
"Whatever happens on the field of play today, Levante are going to take this situation to the Federation tomorrow," Catalan said earlier on Thursday.
"We feel that there is a solid enough precedent to back up the club's decision to do so."
Chumi was banned after he received a yellow card playing for Barcelona's B team in the Segunda B division.
Barcelona, however, insist a change in the rules in November means the suspension does not carry over into the Copa del Rey.
"There were never any doubts about Chumi, none," Barca coach Ernesto Valverde said. "We did everything right. Tomorrow we will be in the draw, we have no doubts, not before and not now."
Levante may feel precedent is on their side after Real Madrid were disqualified from the Copa del Rey in 2015 for fielding Denis Cheryshev, despite the player being suspended.
Madrid had overlooked Cheryshev receiving three yellow cards while playing for Villarreal in the competition the previous season.
"I tried to focus on the game," Levante coach Paco Lopez said. "I understand that the club does what it thinks is right. There are rules we all have to follow."
Barcelona were certainly worthy winners on the pitch at the Camp Nou and, as it stands, will join Real Madrid, Sevilla, Real Betis, Valencia, Girona, Getafe and Espanyol in the last eight of a tournament they won, as well as La Liga, last year.
That domestic double arguably took its toll in Europe, however, and Valverde has been under pressure to afford his key players more rest this season. Barca play Lyon in the Champions League last 16 next month.
Messi started, along with fellow regulars like Jordi Alba, Clement Lenglet, Ivan Rakitic and Arthur. Luis Suarez, Gerard Pique, Sergio Busquets and Marc Andre ter Stegen all began on the bench.
Barcelona were dominant from the outset, as a curling Messi free-kick was pushed wide and Philippe Coutinho, excellent again, shot over.
Messi and Arturo Vidal both went close and finally in the 30th minute, Dembele made the breakthrough, latching onto Messi's pass before bundling the ball into the net.
A minute later, the Frenchman had a second. Coutinho found Messi on the break and he slipped free the sprinting Dembele, who ran round Aitor Fernandez and scuffed the ball home off the goalkeeper's outstretched leg.
Levante were still only a goal away from extra-time but Messi ended any hopes of a comeback. Dembele freed Nelson Semedo down the right and he found the Argentinian in the middle. A chipped finish was all it needed.