With Saturday's Clasico against Real Madrid on the horizon, Luis Enrique made 11 changes to his team and was indebted to teenage debutant Carles Alena for levelling the first-leg clash after David Mainz's opener for the third-tier side.
Barca have now won only two of their past six matches in all competitions and face the prospect of dropping nine points behind Madrid in La Liga this weekend.
"In terms of intensity, I have not seen relaxed players," Luis Enrique said, as quoted by Mundo Deportivo.
"They wanted to win but we have experience in this kind of knockout tie. As much as I'm not happy, we tried to create problems for a team who changed its system to put five players in defence.
"We struggled in the first half, we were pretty bad. In the second half we created more chances and could have won but the tie is open and you have to wait for the second leg.
"Now we focus on one of the best games that can be seen in the championship and we are motivated to face our rivals."Mahrez laughts at Spurs' title collapse
Alena marked his arrival at senior level in style with a sweetly struck 25-yard effort to spare Barcelona's blushes and it is a moment the 18-year-old will evidently cherish for years to come.
"It's a dream debut, I've waited a long time," he told reporters. "It's one of the happiest days of my life.
"The veterans told me to play normally, that I had to prove nothing. With these players everything is easier. I appreciate all the confidence of Luis Enrique."