Elsewhere, a weakened Barcelona were comfortable 2-0 winners at third-tier Ceuta with Maxwell and Pedro netting first-half goals.
La Liga leaders Madrid were keen to avoid a repetition of last year's shock exit to Segunda B Alcorcon, who dumped Manuel Pellegrini's team out at the same stage 4-1 on aggregate.
The attitude of former coach Pellegrini's side was questioned after their 4-0 first-leg defeat and in the build-up to Tuesday's game Mourinho warned a repeat performance would see players dropped for good.
"There was no 'Alcorcon shock'. We played a serious game and the result, bearing in mind it is a knockout competition, is good," the Portuguese told reporters.
"I would sign for the same in every Champions League away leg. With the attitude I saw tonight it won't be a problem to reach the next stage. I'm sure we'll win the second leg."
"It's clear some players haven't had a great game but everyone has tried and I'll go with that," said the coach.
