Valencia, who lifted the trophy on their last appearance in the showpiece match in 2008, will meet 30-times winners Barca in the final on May 25 at Betis' Benito Villamarin stadium.
Marcelino's side fought back from two goals down to snatch a 2-2 draw in the first leg and a goalless home draw would have seen them through on away goals. They appeared set up to absorb the pressure, inviting Betis to have most of the possession.
The visitors had the better of the chances in a tight and tense first period and it took a strong hand from Valencia keeper Jaume Domenech to turn over a shot from Jese, while Betis defender Aissa Mandi headed narrowly wide following a corner.
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Valencia showed more ambition after the interval and went ahead with a well worked move in the 56th minute which saw Kevin Gameiro race into the box and slide the ball across for Moreno to comfortably tuck it into the empty net from close range.
That meant Betis needed at least two goals to progress and, while they continued to monopolise the ball, Valencia controlled the space and rarely looked like letting their lead slip.
Barca, who have won the last four editions of the competition, beat Real Madrid 3-0 away on Wednesday for a 4-1 aggregate victory in the other semi-final.
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