The Spanish champions had taken a seventh-minute lead from Joao Felix, with Elanga levelling with his first touch with 10 minutes to go after Bruno Fernandes’ pass.
The 19-year-old Swedish winger has netted three goals - all in the past two months - in 14 appearances this season, making a major impact in the past week.
“He is playing as if a dream comes true. He is just a joy and it’s fun to watch him play,” United manager Ralf Rangnick told reporters about Elanga.
“I wish a few other players would take him as an example, or almost as a role model I would say, not because he is doing everything right, but because he’s just enjoying himself on the pitch and that’s what its all about.
“Football is an important sport and even more so for our supporters or for the media, but it’s still a ball game and you have to enjoy yourself on the pitch. This is what I wish us to do when we play them again in a few weeks.”
Rangnick was damning of the Red Devils’ first half display at Atletico, claiming they were “too apprehensive” but was bullish given the draw that they could progress with the second leg at Old Trafford.
Elsewhere, Ajax Amsterdam led twice but had to settle for a 2-2 draw away to Benfica, with Sebastien Haller scoring at both ends.