A brilliant Ricardo Oliveira strike sent Valencia back to the top of the Primera Liga with a 1-0 win at Barcelona, while Real Madrid stayed in touch with the leaders thanks to a Ronaldo double in a 2-1 win over Espanyol.
Valencia, 2-0 winners over Real Madrid last weekend, were outplayed by Barca for much of an entertaining Nou Camp clash but the Ches clinched victory with a first-time shot from the edge of the box by Brazilian Oliveira after 15 minutes.
A fifth successive win for Rafa Benitez's side took them back to the summit with 16 points from six matches, one point clear of Deportivo Coruna after their 5-1 home win over Atletico Madrid on Saturday.
Real Madrid remained on the shoulders of the leaders thanks to a decisive contribution from another Brazilian striker.
Ronaldo turned in a cross from Raul in the 53rd minute and made it 2-0 eight minutes from time by meeting David Beckham's precise cross with a downward header.
Alex pulled one back for Espanyol in the third minute of injury time but that proved to be the last kick of the game.
After six matches, Real are three points behind Valencia with 13 points.
Barcelona's first defeat of the season left them down in ninth place with nine points.
Real Madrid were a long way short of their best against Espanyol, who held out until halftime with little trouble.
"We knew it was going to be difficult, with Espanyol giving everything in defence," said Real coach Carlos Queiroz.
"We created far more chances, though, and that makes us worthy winners."
Ronaldo's opener came courtesy of a smart piece of work from Raul, who turned his marker on the right of the area and pulled the ball across for the Brazilian to provide a simple finish.
Luis Figo missed a penalty a few minutes later after Roberto Carlos had been pushed and Real looked to be heading for trouble when Espanyol midfielder Adrian Bastia was brought down in the area by Francisco Pavon.
The referee waved away what looked to be a straightforward penalty appeal, though, and Ronaldo clinched the points with his fifth league goal of the season.
Espanyol had Pierre Wome sent off for a second booking in the 90th minute and a sweet finish from Alex came far too late to inspire a comeback.
Real Sociedad's hopes of launching another title challenge were hit when they could manage only a 1-1 draw at home to Sevilla.
Sociedad, runners-up to Real Madrid last season, took the lead after just four minutes when Valery Karpin crossed from the right for Darko Kovacevic to head home.
Sevilla levelled with a Dario Silva strike on the quarter-hour, though, and Sociedad created little else for the remainder of a disappointing game.
The result left Sociedad in sixth place with nine points, six behind the leaders and ahead of Real Betis, Sevilla and Barcelona on goal difference.
Osasuna continued their solid start to the season with a 1-1 draw away to Real Mallorca that took them up to fourth place on 11 points.