Gerard Pique headed Barcelona in front in the first half, and Alena made the game safe after replacing Arturo Vidal in the second half.
The 20-year-old was put through by a brilliant ball from Lionel Messi but then came up with a superb dinked finish to beat Sergio Asenjo.
| GOAL! |— Eleven Sports (@ElevenSports_UK) December 2, 2018
Lionel Messi threads the eye of a needle, to put Carlos Alena through
The 20-year-old was ice cold in front of goal! ❄️ pic.twitter.com/a9JLWNRBAF
It was some strike from Alena and a great way to seal victory.
We should hopefully get to see him back in action on Wednesday when Barcelona face Cultural Leonesa in the second leg of their Copa del Rey clash.