After completing a four-month biting ban, Luis Suarez made an early impact on his Barcelona debut by setting up Neymar's fourth-minute opener at Real Madrid. Then it started to go wrong for Barca against its fiercest rival in the highly-anticipated "clasico" on Saturday.
Barcelona, which had kept clean sheets in the eight domestic games before Saturday, conceded three times to lose 3-1 at the Santiago Bernabeu Stadium.
On a subdued night for Barca star Lionel Messi, great rival Cristiano Ronaldo started Real's comeback in the 35th minute. The world player of the year's 21st goal of the season came from the penalty spot after defender Gerard Pique stopped Marcelo's cross with his arm.
Pepe punished Barcelona's shaky defending when he headed Toni Kroos' corner into the net five minutes into the second half. And Karim Benzema, who had already hit the woodwork twice, left Real deflated by scoring in the 61st after being set up by James Rodriguez.
With a ninth successive win in all competitions, Madrid moved into second place one point behind Barcelona.
Although Suarez was Barcelona's greatest attacking threat in the Uruguay striker's first competitive match since his World Cup biting incident, he couldn't score during 69 minutes on the pitch.
"I don't regret that he started," Barcelona coach Luis Enrique said of the offseason recruit from Liverpool. "He did more than I expected him to do, and I substituted him for fitness reasons."
Here is a look at the other action from Europe's top leagues on Saturday:
Manchester City and Liverpool endured Premier League frustration following Champions League setbacks.
Having thrown away a winning position to draw at CSKA Moscow in midweek, City was stunned 2-1 by West Ham at Upton Park. Morgan Amalfitano and Diafra Sakho provided fourth-place West Ham with its latest eye-catching win while inflicting City's second loss in its title defense. David Silva scored City's consolation.
City was dislodged from second place by surprise package Southampton, which followed up its 8-0 rout of Sunderland with a more mundane 1-0 win over Stoke after Sadio Mane's first goal for the south-coast club.
While Southampton's start has been astonishing after a summer of upheaval, Liverpool's has been erratic without Suarez. Mario Balotelli, whose performance up front and conduct was decried after Wednesday's 3-0 loss to Real Madrid, failed to score his first league goal for the club in a 0-0 draw with Hull.
But Arsenal hit back after last weekend's draw with Hull, with Alexis Sanchez scoring twice in a 2-0 victory at Sunderland. Arsenal is fifth but Swansea and Liverpool are only behind on goal difference. Wilfried Bony's double gave Swansea a 2-0 win over Leicester.
Borussia Dortmund slumped to its fourth straight league loss as Hannover beat Juergen Klopp's side 1-0.
Japan midfielder Hiroshi Kiyotake struck a free kick over the wall and inside the corner in the 61st minute against the 2011 and 2012 league champions.
Stuttgart won 5-4 at Eintracht Frankfurt, Augsburg defeated Freiburg 2-0, Hertha Berlin routed Hamburger SV 3-0 and unbeaten Hoffenheim beat promoted Paderborn 1-0 to go second behind Bayern Munich.
Sassuolo inflicted Parma's fifth successive loss while recording its first win of the campaign with a 3-1 victory over the bottom-place team.
In the late game, Roma was looking to move provisionally top of the league when it played third-placed Sampdoria. Roma is a point behind three-time defending champion Juventus, which hosts Palermo Sunday.