Everything appeared to be running to plan for the visitors when Miguel Angulo fired Valencia ahead midway through the first half but they were made to pay for their failure to convert their opportunities just before the interval.
Defender Mauricio Pellegrino headed a corner into his own net and then Sergio Corino nodded in the winner ten minutes into the second half.
The result lifts Vallecano off the foot of the table and they also had to survive the final quarter of the match with ten men after Pablo Sanz was sent off.
Athletic Bilbao reignited their faint title hopes with a stunning fightback to beat eight-man Alaves 3-2 in a stormy Basque derby.
Alaves were quickly into their stride with a double from Jordi Cruyff inside the opening 12 minutes putting the hosts firmly in the ascendency.
However, five minutes before half-time, it all went pear-shaped for Alaves as first Magno was sent off and then Tiko pulled a goal back two minutes before the break.
On the stroke of half-time, Ruben Navarro received his marching orders before Ismael Urziaz snatched an equaliser.
With 15 minutes remaining, Oscar Tellez was dismissed for a second bookable offence, then Aitor Larrazabal slotted home the match-winning penalty.
Celta Vigo were also 3-2 winners but they were forced to work hard for their victory against lowly Las Palmas.
Catanha and Alexander Mostovoi put Celta in the driving seat before second half goals from Orlando and Paqui squared matters until Valery Karpin snaffled the winner with 13 minutes left.
Real Betis slipped up at Real Zaragoza as they had to rely on Dani's 70th minute equaliser to earn a point after Mate Bilic had put the hosts ahead on 24 minutes.
Real Sociedad hauled themselves out of the bottom three with a much-needed triumph over Espanyol, which was secured via Darko Kovacevic's first half strike.
Malaga moved into the top half of the table with a 2-0 success at Sevilla as Julio Cesar Dely Valdes struck twice in the second period.
Valladolid appeared primed for a valuable away win after early goals from Fernando and Luis Garcia put them in control at Villarreal.
But the home team produced a late comeback to earn a point with Javier Calleja and Rodolfo Arruabarrena on target.
In a dour game in the Canary Islands, Tenerife failed to boost their survival hopes as they were held to a 0-0 draw by Mallorca.
Click below for an individual match summary:
Alaves 2-3 Athletic Bilbao
Celta Vigo 3-2 Las Palmas
Rayo Vallecano 2-1 Valencia
Real Sociedad 1-0 Espanyol
Real Zaragoza 1-1 Real Betis
Sevilla 0-2 Malaga
Tenerife 0-0 Mallorca
Villarreal 2-2 Rayo Valladolid
