Ruben Castro was the visitors' hero, the striker swooping just a minute from the end to send the home crowd away disappointed.
Victory for Betis doubled their points tally for the fledgling season and Pepe Mel's side now sit in sixth, like Valladolid on six points, but ahead on goal difference and with a game in hand.
The match appeared to be heading for a stalemate until Castro won possession in the penalty box and fired a low shot past the hosts' goalkeeper Jaime.
Valladolid had enjoyed the better of the opening stages before Betis grabbed a foothold in the game, although neither side could find a way through.
An action-packed finale to the match though led to chances for both teams to grab a late winner.
It was Castro who proved decisive in the end, although Valladolid came close to an even later equaliser when Ebert fired wide from long range in injury time.