The hosts started superbly and they were rewarded for their early pressure in the ninth minute when Salva Sevilla created space on the edge of the box before firing a low shot past Diego Alves.
Betis had chances to extend their lead in the first half, with the best opportunity going to Joel Campbell, but the striker failed to find the target with a free header.
Alves came to the rescue for Valencia after the break by reacting well to block Ruben Castro's curled effort from the corner of the box.
Roberto Soldado wasted a chance to equalise midway through the second period when he found space inside the Betis area but his weak effort was easily stopped by Adrian.
Valencia continued to search for a goal until the final whistle and had an opportunity when Jonathan Viera found Nelson Valdez at the back post but the substitute's header was wayward and Betis held on for the three points.