Javier Aquino scored deep into stoppage time to earn Villarreal a 2-2 first-leg draw on Friday, with Sergio Pelegrin and Richmond Boakye having earlier eclipsed Giovani dos Santos' opener.
They will meet again for the second leg at the Estadio Manuel Martinez Valero on December 17 but, despite having home advantage, Escriba considers his men to be underdogs.
"This tie is very much in the balance and it will be a very tough return leg, although I still see them as favourites," he said.
"At 2-1 it was a good result for us but they had a couple of chances through direct balls and managed to get a draw, but these things happen in football.
"In the opening 45 minutes they had more opportunities and after the break the game evened out. In the end they scored in stoppage time but we could have got a third."
Elche, 11th in La Liga, travel to Levante before the return leg, while Villarreal face a daunting trip to defending champions Barcelona.
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