Nacho left his team mates stunned as he tried to clear a cross in the 13th minute and headed the ball into the net.
Lionel Messi has added another record against his already legendary name.
Paris St Germain made light of the absent Zlatan Ibrahimovic and a sub-standard start to the season to claim a 3-2 Champions League victory over Barcelona on Tuesday.
A week ago, Barcelona still had a chance of repeating the historic treble of 2009 but defeats in Europe and La Liga mean Wednesday's King's Cup final against Real Madrid may be their only hope of major silverware this season.
The Swedish striker's contract was extended for an extra year despite him missing the rest of the season due to a serious knee injury.
Livepool striker and Dembele close in on Camp Nou move
Barcelona seized control of their King's Cup quarter-final tie against Atletico Madrid when Lionel Messi followed up his saved penalty to score and secure a 1-0 first-leg victory at the Nou Camp on Wednesday.
Bayern Munich will not only have to overturn a 3-0 Champions League semi-final first leg deficit against Barcelona on Tuesday but they will have to do it against a superb defence and in the midst of their biggest slump in years.
Neymar took time to settle but is finally shining in Barcelona's devastating attacking trident with Villarreal the next La Liga opponents in their sights on Sunday as the Catalans continue their pursuit of Real Madrid.
Barcelona and Lionel Messi can write new chapters in the record books on Tuesday if they are able to break out of the straightjacket imposed on them by AC Milan and reach the Champions League semi-finals.
Real Madrid's hopes of overhauling La Liga leaders Barcelona suffered a stinging blow when they were held to a 2-2 draw at home to Valencia.
A summary of Thursday night's UEFA Champions League matches.
Lionel Messi fittingly sealed Barcelona's 26th La Liga title on Saturday by coming off the bench to score the goal in a 1-0 win over Levante in front of a jubilant Nou Camp crowd, who celebrated a remarkable eighth league crown in 11 years.
Barca looked set for a third consecutive league draw as they created scant opportunities but they were presented with the advantage of an extra man when Villarreal midfielder Daniel Raba was given a straight red card for a wild, studs-up challenge on Sergio Busquets on the hour mark.
The 23-year-old will inherit the number 10 shirt from the departing Argentine Juan Roman Riquelme.
Real Madrid moved seven points clear at the top of La Liga with a comfortable 3-1 win over bottom side Real Zaragoza as Barcelona could only draw 0-0 at lowly Villarreal on Saturday.
Neymar scored the opener to continue his rich vein of form as 10-man Barcelona won a one-sided La Liga derby against Espanyol.
Lionel Messi and some of his Barcelona colleagues paid warm tribute to teammate Xavi on Friday after he extended his appearances record to 700 in the midweek King's Cup match at Getafe.
Barcelona winger Raphinha secured a 1-0 win in LaLiga for the second straight week this time at Athletic Bilbao as his side tightened their grip on top spot.
With five titles, Barca are now level with AC Milan on all-time UEFA Super Cup winners list
'We want to clarify that our desire has always been to apply a drop in salary because we fully understand that this is an exceptional situation and we are the first ones who have ALWAYS helped the club when asked'
Barcelona president Joan Laporta has received a number of death threats in recent weeks and has reported them to the police, he said on Saturday.
Barcelona closed in on the La Liga title by thrashing local rivals Espanyol 5-0 on Sunday as Atletico Madrid dropped out of the race after losing 2-1 at Levante and Real Madrid beat Valencia 3-2.
The rest of Barcelona's squad will have to do "a little bit more" to make up for the absence of five-times World Player of the Year Lionel Messi for the next three weeks, according to captain Andres Iniesta. The Argentina forward faces a spell on the sidelines after sustaining a groin injury in Wednesday's 1-1 La Liga draw with Atletico Madrid. "There's no question we are stronger with Messi," Iniesta told Cadena Cope radio ahead of Saturday's match at Sporting Gijon. "When these things happen we all have to give a little bit more.
Lionel Messi completed a sparkling performance by chipping the goalkeeper from the edge of the area as Barcelona swept aside ten-man Levante 5-0 away on Sunday to continue their winning start at the top of La Liga.
Barcelona are in the unusual position of having drawn their last three matches as they prepare for Saturday's home La Liga game against Real Sociedad and Pep Guardiola's unwillingness to commit to a new contract is not helping settle jangled nerves.
Defender Gerard Pique grabbed a rare winner and Lionel Messi scored yet another beauty as Barcelona came from behind to beat Sevilla 2-1 at the Nou Camp on Sunday and reclaim an eight-point lead at the top of La Liga.
Saturday marks the 10th anniversary of Lionel Messi's first-team debut with Barcelona, when the Argentine came on as a 16-year-old substitute during a friendly against Porto in Portugal.
Barcelona retained the King's Cup with a 2-0 victory over Sevilla to complete a domestic double.
Cesc Fabregas and Alexis Sanchez were on scintillating form as leaders Barcelona made light of the absence of injured World Player of the Year Lionel Messi with a 5-0 win at home to Real Mallorca in La Liga on Saturday.
Holders Barcelona cruised into the King's Cup quarter-finals when a side missing several regulars beat city rivals Espanyol 2-0, with Munir El Haddadi netting both goals in a thumping 6-1 aggregate success on Wednesday.
A delightful flick and volley from Neymar allowed him to complete a double as Barcelona beat Villarreal 3-0 to go three points clear at the top of La Liga ahead of Real Madrid's clash with Sevilla later on Sunday.
'Will I be playing at Barca next season? It's an unknown'
Manchester City swept aside second-tier Cardiff City 2-0 with first-half goals from Kevin De Bruyne and Raheem Sterling on Sunday to reach the FA Cup fifth round in their quest to win an unprecedented four trophies this season.
Lionel Messi scored one penalty and missed another as Barcelona beat Real Valladolid 1-0 on Saturday to open up a seven-point lead at the top of La Liga.
Holders Barcelona will begin their defence of the Champions League with a home match against AC Milan after the two old rivals were drawn in the same group on Thursday.
Seydou Keita hit a hat-trick and Zlatan Ibrahimovic netted twice to lead Barcelona to a 6-1 thrashing of Real Zaragoza and send the La Liga champions three points clear of Real Madrid on Sunday.
Now, Real Madrid have never won the Spanish treble and are fighting tooth and nail in La Liga to prevent arch-rivals Barcelona scooping Champions League and domestic league and Cup titles for a second time.
Lionel Messi came off the bench and scored twice in the second half as Barcelona, who survived two late dismissals, won 2-1 at Racing Santander on Sunday and maintained their huge lead in the Primera Liga. Racing gave the visitors little space and took the lead after the restart when Nikola Zigic scored from the penalty spot.