Valencia sent shockwaves through La Liga by coming from behind to end Real Madrid's record-breaking winning streak with a 2-1 victory at the Mestalla.
Cristiano Ronaldo's penalty had put Los Blancos on course for a 23rd straight victory in all competitions, but the hosts struck twice in 13 second-half minutes to claim the honour of halting the run.
Manchester City loanee Alvaro Negredo was adjudged to have handled the ball inside the box on 14 minutes, and Ronaldo was never going to miss.
It was the Ballon d'Or favourite's 33rd goal in 25 club appearances this season and came via the first clear-cut chance of a somewhat scrappy opening.
The Portuguese should have perhaps doubled his tally and Madrid's cushion when he ran on to a through-ball from Gareth Bale and rounded Valencia stopper Diego Alves, only to shoot into the side-netting.
Valencia finished the half strongly and twice came close to an equaliser as Pepe produced a crucial block to deny Antonio Barragan, and Andre Gomes struck the post with an effort which had Iker Casillas beaten.
The hosts continued pushing forward after the interval as a confident half-volley from Gomes dipped just wide of the post, and soon did grab their deserved equaliser courtesy of some Madrid assistance.
Full-back Barragan advanced into the box once more on 52 minutes and, while Pepe was again across to get in the way of his shot, the ball deflected off the visiting defender and into the back of the net.
After Bale had squandered a chance to restore Real's lead by shooting at Alves when Karim Benzema was better placed, Nicolas Otamendi headed in Daniel Parejo's corner to complete Valencia's turnaround.
Madrid's feathers were well and truly ruffled and they could have been 3-1 down when Barragan nearly fired the ball into the bottom corner after another rampaging run into the Real box went unchecked.
A response from Carlo Ancelotti's side was a while in coming, but they did have several good chances to peg Valencia back in the final stages, with Sergio Ramos sending a free header narrowly wide of the post.
They were to come closer still when Isco guided Dani Carvajal's 85th-minute cross towards goal. Alves blocked, but still required Otamendi to rescue him by hooking the ball away off the line.
Madrid's first defeat since September 13 opens the door for Barcelona to leapfrog them with victory over Real Sociedad tonight, while the victory takes Valencia fourth and to within five points of the La Liga leaders.
