Atleti head to Catalonia on Saturday for a mouth-watering clash against Ernesto Valverde's side, who saw their lead at the summit cut to eight points after a sensational 4-4 draw against Villarreal, last-gasp goals from Lionel Messi and Luis Suarez rescuing the champions.
Simeone told a media conference after the win against Girona: "We have to stay as high as we can. We will try to win [at Barcelona].
"The important thing is that we are all together. Whether it's a coach or a player, since I came to the club I have always seen that the important thing was that union."
Atletico made a laboured start amid distracting scenes in the stands, as fans staged a 12th-minute walk-in protest due to a perceived lack of appreciation from the players following the Champions League defeat to Juventus.
Simeone was happy with how his side grew into the game, though, and thinks they were good value for the three points.
"Except in the first part of the game, in which one of their strikers had a clear header, we were comfortable," he said.
"We had chances to score, hit the post, there was a possible penalty on Alvaro Morata, two or three shots from Griezmann. We felt that we were dangerous when we attacked.
"After the break we didn't play well but our changes revitalised us. I think that was what brought us closer to the goal.
"They tried to counter attack and wait for us to make a mistake and we tried to find the goal despite the limited spaces that we found. In the end we found it though."