Since becoming Atleti coach in 2011, Simeone has overseen a title triumph and two runs to the Champions League final, but his side have had to fight hard for a place in the top four this term.
"We can talk about ourselves because we had a really tough end of the last season — I have always said that," he told a post-match news conference.
"I think this season is the most difficult since I have been here at the club. We have had so many injuries with [Jan] Oblak, Augusto [Fernandez] and Tiago.
"Atletico couldn't win at the beginning of the season, but we could reinvent ourselves in order to turn the situation around. I think the team is fitter, but we have to be quiet because there are 10 matches left."
Simeone hopes his side can close in on securing a top-four spot and took encouragement from beating a third-placed Sevilla side who he feels are enjoying a "great season".
"It's clear we have a seven-point gap to fifth because Villarreal and Real Sociedad couldn't win and that's important for us," he added.
"I think Sevilla are having a great season, they are praised by the press and all the world, so I think this result shows our value — we believe this is the level to follow and we look ahead."
But captain Gabi wants Atleti to chase down Sevilla after this result, with the gap between them down to just two points.
"These were three vital points, and three points that change our objectives for the season," he said.
"We're secure in fourth place now and we're going to go for third.
"It was a very complete game from the whole team, we're happy with the result."