Real Madrid stumbled to a 1-1 draw at home against Valencia in the opening match of their Spanish league title defence on Sunday.
Madrid appeared set to pick up where they had left off last season when Gonzalo Higuain scored in the 10th minute, but Jonas levelled for Valencia in the 42nd to give coach Mauricio Pellegrino a hard-earned draw on his debut.
In the later game Barcelona thrashed Real Sociedad 5-1 with Lionel Messi scoring twice.
To sweeten the debut of Barcelona coach Tito Vilanova, David Villa played his first competitive minutes since breaking his leg last December and capped the win with a goal.
Also, Real Betis defeated Athletic Bilbao in a 5-3 shootout at San Mames stadium after the Basques had fought back from a three-goal deficit to draw level.
Cristiano Ronaldo, who set a club record with 46 league goals last season, was uncharacteristically subdued and failed to manage a shot on goal.
"We knew it was going to be tough because Valencia has played well here before,'' said Madrid defender Raul Albiol, who formerly played for Valencia.
"We have to stay positive and look forward.''
Madrid dictated the pace early on and Higuain, starting ahead of Karim Benzema, soon put his team ahead.
Higuain scored on the third attempt after goalkeeper Diego Alves made back-to-back saves to deny the Argentina striker. International teammate Angel di Maria lofted a pass behind Valencia's passive defence, Higuain pulled it in and blasted the second rebound into the back of the net.
Just when Valencia appeared clueless in attack, Brazil forward Jonas levelled for the visitors with a header, beating three Madrid players to Tino Costa's in-swinging free kick. Madrid goalkeeper Iker Casillas and defender Pepe collided in an attempt to reach the ball, with both lying prone on the pitch for a few moments before restarting play with both looking groggy.
Albiol replaced Pepe at half-time.
Jonas' goal was Valencia's first in their last five league visits to Santiago Bernabeu stadium. The score level, Valencia regained their composure and succeeded in slowing down a Madrid attack that last season set a league scoring record with 121 goals.
Madrid coach Jose Mourinho sent on Benzema for midfielder Lass Diarra, looking to spark his team with 30 minutes to go.
Higuain and Di Maria almost linked up again in the 65th when Di Maria lobbed a perfectly placed ball to his teammate, only to see Higuain's header hit the crossbar.
That miss was as close as the champions came to scoring again with Valencia defending well down the stretch.