Los Che surrender a goal advantage in the final minutes to end a forgettable week for Unai Emery's side which has seen them knocked out of the Champions League
Los Che had been heading to their third consecutive win after Jose Dorado had gifted them the lead with a own goal midway through the second half. But the Verdiblancos continued to fight until the final whistle and Ruben Castro scored twice in injury time to record a stunning finale to the match.
The first 45 minutes belied the club's current form in La Liga as Betis proved the more dominant, although it was Valencia who tested the Andalusians resolve first.
Roberto Soldado latched onto Tino Costa's quick through ball but his effort from an acute angle was pushed away by Castro at his near post.
Pepe Mel's side then began to show their attacking ambition as Roque Santa Cruz went close to opening the scoring. The former Manchester City striker burst onto Ruben Castro's cross in the penalty area but was crowded out by a mass of Valencia defenders.
After the break, Betis began to formulate chances more freely as the match progressed and Ruben Castro should have fired them ahead but he fired his shot wildly off target.
Unai Emery's side responded well, and Jonas went close with a placed shot from the edge of the box prior to Soldado's coming within a whisker of converting Antonio Barragan's low cross.
Valencia had steadily began to assert themselves in the match and they took the lead when Dorado inadvertently diverted the ball into his own net. Costa's through ball picked out Jeremy Mathieu whose precise cross was turned home by the Betis defender.
Betis showed admirable spirit as they went in search of an equaliser, and they were deservedly reward when Castro was able to turn home Juanma's deflected cross.
The pair combined two minutes to seal a dramatic win for Pepe Mel's side as Castro sprung clear of the defence before unleashing a thunderbolt into the back of the net.
Valencia next welcome Malaga to San Mames as they look to recover from a shocking turnaround, whilst Betis' match against Atletico Madrid will not be able to come quick enough for Pepe Mel's side.