After a limp first half, Wasl were much sharper in the final 45 minutes, scoring in the 69th minute when Rashed Essa headed in a cross from Francisco Yeste. The Dubai club continued to apply pressure in the final 20 minutes but could not force the game to extra time.
Wahda, the defending Pro League champions, will have a chance to win the UAE's equivalent of the FA Cup for the first time since 2000 when they meet the winner of tonight's Al Jazira-Al Shabab semi-final match.
The victory was a significant one for Wahda, who were knocked out of the Etisalat Cup semi-finals and are buried 14 points behind leaders Jazira in this year's Pro League chase.
Wasl have exited both cup competitions in the semi-final stage and it now must regroup to push for a top-three finish in the Pro League, which would yield a potential berth in next year's Asian Champions League competition.