Real Madrid's title hopes suffered a huge blow after they slumped to a 1-0 defeat at the hands of lowly Osasuna at the Reyno de Navarra stadium.
Javier Camunas' goal just after the hour-mark consigned Madrid to only their second league loss of the season, but one that leaves Jose Mourinho's men seven points behind rampant leaders Barcelona.
That gap is also essentially eight points with Madrid having lost 5-0 to Barca at the Nou Camp and needing something approaching a miracle to gain the better head-to-head record when they host the Catalan side in the re-match at the Bernabeu.
Madrid will have been well aware of the threat posed by 17th-placed Osasuna having been held to 1-1 draw by then-bottom side Almeria in their previous away game, while the Pamplona outfit have also made things very difficult for the capital club in recent meetings between the two.
Osasuna, who had picked up just three points from a possible 24 over the last month, were the first to threaten with Ferran Coro driving a shot just wide early on.
Walter Pandiani also missed a good chance for the hosts in the 32nd minute when he escaped his marker but glanced Camunas' cross over from eight yards out.
Madrid also had their chances in the first half as well though, with Karim Benzema and Cristiano Ronaldo both being denied by good saves by Ricardo Lopez in the home goal.
Ronaldo drove another shot just inches wide of the far post 10 minutes into the second half, but Mourinho's side were stunned in the 62nd minute when Osasuna took the lead.
Pandiani headed on a long ball to strike partner Carlos Aranda, whose poked pass put Camunas through on the edge of the area and, as the visiting defence appealed in vain for offside, the Madrid-born forward fired his shot in off the inside of the far post.
Mourinho responded to that by making an attacking treble change, sending on new loan signing Emmanuel Adebayor for his debut, as well as Kaka and Xabi Alonso, with Lassana Diarra, Raul Albiol and Angel Di Maria the men to make way.
The adventurous new-look Madrid line-up then laid siege to the Osasuna goal, but Ronaldo, Benzema and Mesut Ozil all failed to hit the target with efforts before Ronaldo finally tested Ricardo with a low shot.
Madrid almost found themselves 2-0 down in the 83rd minute when Aranda skipped past two challenges on the goalline before laying the ball back to substitute Krisztian Vadocz seven yards out.
With Iker Casillas already committed to blocking Aranda's run a goal looked a certainty, but Alvaro Arbeloa got back to make a sliding goal-line block to deny Vadocz.
That gave Madrid a lifeline to get something out of the game, but - despite five minutes of stoppage time - they could not a find a breakthrough and now face an uphill battle if they are to win a first Primera Division title since 2008.