Real Madrid have one hand on a first La Liga trophy in four years after Cristiano Ronaldo scored a brilliant winner in a 2-1 victory at Barcelona on Saturday that stretched their lead over their bitter rivals to seven points with four games left.
On a dramatic, rain-lashed night at the Nou Camp, the Portuguese forward's 73rd-minute strike from Mesut Ozil's superb assist secured the win his coach and compatriot Jose Mourinho had sought in vain in eight previous trips to Barca's imposing arena during his otherwise glittering career.
It was Real's first success in eight La Liga 'Clasicos' - four of them before Mourinho arrived from Inter Milan - and gives them a timely boost for Wednesday's Champions League semi-final second leg at home to Bayern Munich, when they will seek to overturn a 2-1 deficit.
"We have struck a very significant blow but it's not yet decisive," Real midfielder Xabi Alonso said in an interview with Spanish television.
"Of course it's an important step towards the title but now we have to see it home," added the Spain international.
"Cristiano's goal, coming straight after they levelled, broke their stride and that was fundamental.
"We controlled the match perfectly. It was a great performance, a fantastic result and I am very happy. Now we have another key match on Wednesday."
Barca, by contrast, need to regroup after suffering back-to-back defeats for the first time in almost three years following Saturday's reverse and a 1-0 loss at Chelsea in their Champions League semi-final first leg on Wednesday.
Pep Guardiola, whose only defeat in 14 previous 'Clasicos' as Barca coach was in last year's King's Cup final, may also have his tactics questioned after he left Alexis Sanchez, Cesc Fabregas and Pedro out of his starting lineup.
Sanchez came off the bench to snatch a 70th-minute equaliser after a rare Sami Khedira goal had given Real an early lead, while a toothless Barca could have done with Fabregas's creativity and eye for goal much earlier than the 80th minute.
Guardiola opened his news conference by conceding his bid to lead Barca to a fourth straight La Liga crown had failed.
"I congratulate Real Madrid on their victory and on the league title," the former Barca and Spain midfielder said.
"Right now the players are tired and sad and I can't say if there will be a psychological effect for the Chelsea game," he added.
"We will try to find a way to attack Chelsea but now we have to rest and recover and try to forget tonight's game as quickly as possible."
As the two teams walked out for a match watched by hundreds of millions around the world, close to 100,000 home fans transformed the stadium into a giant mosaic in the blue and red colours of the club and the yellow and red of Catalonia.
"Som i serem" (We are and we will be) was picked out in yellow on one side of the arena as the home support bellowed the club anthem "El Cant del Barca".
Guardiola deployed an attacking formation with only three defenders and featuring the surprise inclusion of pacy 20-year-old B-team winger Cristian Tello.
Mourinho fielded the same starting 11 as he did on Tuesday, when Real were beaten 2-1 at Bayern Munich, with Ronaldo, Karim Benzema, Angel Di Maria and the excellent Ozil looking to catch Barca on the break.
Real, who also set a new record of 109 goals scored in a league season, were ahead when Khedira was sharpest to react after Barca goalkeeper Victor Valdes could not gather the ball after a corner and the Germany midfielder bundled it over the line.
Barca had started nervously and lacked their usual fluidity, and once Real were ahead they defended solidly and rarely looked like conceding as Barca stroked the ball around on the slick surface without real penetration.
The noise volume inside the giant arena rose after substitute Sanchez finally scrambled the ball in for the equaliser but the home fans were silenced three minutes later.
Ozil's superb pass released Ronaldo in space on the right and he took the ball wide before smashing it home.
The goal, extending his La Liga record tally for the season to 42, was the best response to critics who accuse the Portuguese of flopping in big games. He is now one goal ahead of Barca forward Lionel Messi at the top of the scoring chart.
Messi tried desperately to breach the Real defence but was thwarted again and again and cut a forlorn figure at the end of the game as the Real players celebrated wildly nearby.
As well as virtually wrapping up the title, Real's win ended Barca's 11-match winning streak in the league and inflicted a first defeat on the Catalans in 35 league matches at the Nou Camp and in 55 home games in all competitions.
Mourinho, who again declined to speak to the media, will now be relishing a potential crack at his old club in next month's Champions League final in Munich.
Stats from Saturday's La Liga match between Barcelona and Real Madrid at the Nou Camp.
* Cristiano Ronaldo scores his 54th official goal of the season, breaking his personal record from last year.
* Barcelona 1 Real Madrid 2: Cristiano Ronaldo sets a La Liga record by scoring his 42nd of the season.
* Barcelona 1 Real Madrid 1: Alexis Sanchez with the equalizer. He also scored in the first leg at Bernabeu. Jeffren was the last Barca substitute to score in a La Liga Clasico (29 Nov 2010).
* The last season in which both Clasicos in La Liga resulted in away victories was also the last season in which neither Real Madrid nor FC Barcelona won La Liga. Valencia CF managed that feat in 2003/2004.
* Barcelona are undefeated in their last 34 La Liga home matches (31 victories, three draws, zero defeats) after losing their home opener 2-0 to Hercules last season.
* Jose Mourinho is coaching in his 10th Clasico and he has won only one of the previous nine (four draws and five defeats), emerging victorious in the 2010/2011 King's Cup final, 1-0 at Valencia's Mestalla stadium. Mourinho's Real has been outscored 21-11 in those nine matches.
* Barcelona 0 Real Madrid 1 halftime: The last time Real Madrid led at halftime in a Clasico match at the Nou Camp they won the match (1-0 on Dec. 23 2007). That was also their last victory at Barcelona.
* Barcelona have won four La Liga matches this season after trailing (in each case trailing by 1-0).
* Real Madrid also went in front in the reverse fixture against Barcelona, only to lose by 3-1.
* Barcelona 0 Real Madrid 1: That is the record. 108 goals in a La Liga season is a new single season record. Sami Khedira with his first career goal in a Clasico.
* In 218 official matches between these two sides, the head-to-head record is perfectly balanced. Both sides have won 86 encounters each and there have been 46 draws.
* If Barcelona win tonight, they will be leading the series of official La Liga encounters (deadlocked at 86-46-86 currently) for the first time in 80 years. They led it as recently as January 1932, when their last lead in the head-to-head was taken away by Real Madrid.
* Lionel Messi and Cristiano Ronaldo have both scored 41 La Liga goals this season and have both broken the single season record of 40 goals established by Ronaldo last season. The Portuguese has become the only player that has scored at least 40 in successive league seasons in one of Europe's top five leagues.
* Lionel Messi has scored 63 official goals this season, four shy of Gerd Muller's single season record for a European club (67 for Bayern Munich in 1972/73).
* Of their 57 official matches this season, Lionel Messi has played in 53, at least five more than any of his teammates. He missed both cup matches against Hospitalet, the final group stage match in the Champions League (v BATE Borisov) and missed the March 3 La Liga match against Sporting Gijon due to suspension.
* Barcelona are undefeated in league matches at home this season. In 16 La Liga matches at the Nou Camp in 2011/2012 they have won 15 and drawn one. Sevilla (0-0 on 22 October) were the only visitors to escape defeat so far. Barca have outscored their guests 64-8 this season in the league
* Both teams lost in the Champions League in midweek. The last time the two entered a Clasico match each on the back of defeats was going into the second leg of the CL semi-finals (May 3, 2011) last season. The two had lost in La Liga on April 30, 2011, Barcelona 2-1 away against Real Sociedad and Real Madrid 3-2 at home against Real Zaragoza.
* Barcelona have trailed Real Madrid by as many as 10 points this season. If three points would have been awarded for a victory always, the last time such a big deficit was erased was in 1991/1992 when Barcelona trailed Madrid by 13 (recalculated) after 14 matchdays and won the championship at season's end. So, 20 years ago.
* Barcelona are hoping to win their fourth successive La Liga crown, a feat established only once in club history. The legendary 'Dream Team' of the early 1990s (1991-1994) managed that and Pep Guardiola was a part of that team as a player. The record for most successive La Liga championships is five and was established on two occasions by Real Madrid (1961-1965 and 1986-1990).