Both Elanga and Brandon Williams featured for United, having been on the bench the previous evening for United's Europa League win against Granada.
Elanga made an excellent run down the left side before cutting in and bending the ball into the top corner to double the Reds' lead. But the Swede was upstaged by 18 year-old Ademipo Odubeko - a former United teammate.
The teen struck a superb hat-trick against his old club to earn the win for the Irons.
Afterwards, Elanga told MUTV: "We wanted to win and I think we played well for a lot of the game. We created enough chances to see the game out but it wasn't to be.
"I've been out for a long time and that's what I wanted [to score] to do.
"Getting off the flight this morning, I just wanted to get out there and play, it's been so long," he added.
Although the overall result was poor, Elanga shared his delight at his first-team experience in Spain on Thursday.
"Being away with the first team has been an amazing experience, from travelling with them and being around them in the changing room. It made me hungry to improve and to get better and better.
"To score that goal tonight, it felt really good and you can tell from my celebration it was a relief for me."