Alvarez struck on 90 minutes for the 1-0 victory.
Simeone said: "They are special players. We need time for him and (Alexander) Sorloth to find partnerships. We are working hard as a team, but we need to improve our partnerships.
"It is up to me who can form better partnerships, we will look for that because the lads are ready for anything. Today, with great patience, we took three points from a rival that had not lost since February. We knew that whoever made a mistake would lose. This time we had the chance to score.
"We've been working very well. Except for the first half against Rayo. We need to improve our offensive partnerships. It's good for us to win this game because Barça have taken 21 points and we have to congratulate them because they're doing very well.
"In the first half we didn't create any situations for anything to happen, they defended well. In the second half they fed us with the changes with Rodrigo, Julián, Correa, the entrance of Llorente in the wing. They fed us with more things. They had it before us, but Griezmann and Julián found us and took the three important points that were at stake."