Ten-man Real Madrid slumped to a dire 0-0 draw at Osasuna in the Spanish league as coach Jose Mourinho failed to compensate for the absence of top scorer Cristiano Ronaldo on Saturday.
With Ronaldo serving a one-game suspension, Madrid's pedestrian attack didn't manage a shot between the posts until injury time and was lucky to avoid a loss to the relegation-threatened Osasuna.
Mourinho sent on Karim Benzema, Mesut Oezil and Kaka as luxury reinforcements to try and jump start his attack after halftime, but Kaka lasted 18 minutes on the pitch before receiving his second booking in the 76th minute and his teammates never seriously threatened.
"Maybe we were lacking some spark tonight," said Madrid defender Raul Albiol. "Even though we are way behind Barcelona, we wanted to win the game."
Elsewhere, three homes teams earned wins as Valencia beat Sevilla 2-0, Valladolid downed Mallorca 3-1, and Espanyol edged out Celta Vigo 1-0.
Madrid is in a distant third place with only one win in its last four league games. The draw left it 15 points behind Barcelona before the league leader visits Malaga on Sunday.
If Barcelona wins at La Rosaleda Stadium, 18 points would be Madrid's largest deficit since it was 20 points behind league-leading Atletico Madrid in May 1996.
"I don't want to explain why we can be 18 points behind Barcelona," Mourinho said.
"Things happened in the first weeks that I don't want to talk about. Then, with the gap already large, one team has the pressure while the other doesn't," he said, apparently forgetting that Atletico Madrid is also ahead of his team in the table.
For weeks, Madrid's coach and players have acknowledged that its chances of defending the league title were virtually gone, but Saturday's drab performance - Ronaldo or no - was by far the worst of its disappointing season.
Mourinho has turned off many of Madrid's fans in recent weeks by benching veteran goalkeeper Iker Casillas. Casillas was back in goal with Adan Garrido suspended, but Madrid's latest slip will give Mourinho's critics only more ammunition.
"You never hear me use injuries to my players as an excuse and I won't do it with suspended ones now," the Portuguese manager said.
Madrid showed that it needs Ronaldo for more than just his 16 goals in league play. It also apparently depends on the Portugal forward for its attack to rise above mediocrity.
Ronaldo may not have been there, but Madrid is not poor as high-priced talent goes. Still, even with Argentina forwards Gonzalo Higuain and Angel Di Maria supported by Luka Modric and Xabi Alonso it couldn't create scoring opportunities.
"(Ronaldo) is the best or among the best players in the world and he makes a big impact for Madrid," said Osasuna goalkeeper Andres Fernandez. "I don't think they were comfortable. It was difficult for them to get into the match, and that is to our credit."
After a drab first half by both sides at Reyno de Navarra stadium, Osasuna's Kike Sola finally recorded a shot between the posts moments into the second half when Casillas was forced to block his shot.
Only Osasuna's poor finishing touch saved Madrid from a loss as the hosts claimed the initiative but couldn't take the winner.
Roberto Soldado scored two goals off corner kicks to give Valencia a 2-0 win over visiting Sevilla as it confirmed its turnaround under coach Ernesto Valverde with a third straight win.
Valencia provisionally rose into seventh place, while Sevilla stayed in 12th with only one away victory in nine games.
Valladolid forward Patrick Ebert returned from injury in fine fashion by scoring two goals and setting up the late winner against struggling Mallorca.
Espanyol, meanwhile, escaped the relegation zone after beating Celta at Cornella-El Prat Stadium thanks to Sergio Garcia's first-half goal.
Atletico hosts Real Zaragoza on Sunday, while Real Betis plays Levante, and Deportivo La Coruna is at Real Sociedad. Getafe hosts Granada on Monday.
Rayo Vallecano extended its winning streak to four games by beating Athletic Bilbao 2-1 on Friday.