The striker struck in the 69th minute, shortly after coming on, to settle a contest in which Elche enjoyed plenty of possession but struggled to turn their territorial advantage into goals.
Valencia coach Javier Aguirre was relieved to secure three points after a difficult week, particularly given the impact of the late defeat against Villarreal.
"Much, because the last result did us a lot of damage. It has been a difficult week, but the players have a lot of desire. It is a step forward. They really want to get out of this situation," he said.
Aguirre felt his side had been too hurried in possession during the first half, allowing Elche to dominate territory and apply pressure.
"We talked about how we were losing the ball too easily. In the first half it was pass, pass, pass, and that creates a lot of pressure. Elche take you from one side to the other and put crosses in. We were under a lot of pressure."
His message at half-time was simple: retain possession, find a safe pass and string together several passes to give Valencia greater control.
"I told them to stay calm, to play, to look for a safe pass. Win the ball back, safe pass, three passes. We didn't look like a Primera División team, but the players understood that was the way forward. The substitutions helped too, and we took that step."
Sadiq's return was particularly welcome for Aguirre, who also pointed to the benefit of having other players available again.
"It is a joy, of course. It is important to have him. Rioja is also back, after being out for a long time. Several players have returned. We have a wider range of options now."
Elche coach Martín Anselmi was disappointed that his side had failed to take anything from a match in which he felt they had largely imposed themselves.
"The team did what it had to do on the pitch. We were protagonists, playing in the opposition's half for almost the whole match. We made substitutions to have more presence inside the area," he said.
"When opponents come to the Martínez Valero, they are cautious and show us a lot of respect. We know there are few chances and we have to take them, because we know they might have one."
Anselmi also felt his players needed to circulate the ball more quickly when facing a deep defensive block.
"When an opponent sits back, you have to be closer together to move the ball. Be quicker, play wide, make runs and take risks with certain passes. The few chances you get, you have to hurt them."