A 4-0 victory over Real Sociedad sent Atletico three points clear at the top of the league, with previous leaders Barcelona having lost at home to Valencia on Saturday.
And Diego - who moved to the Spanish capital on a loan deal from Wolfsburg in January, having previously enjoyed a loan spell at the club in 2011-12 - feels such success has been a long time coming.
"It was about time this team grew and won," he said. "When I first came here (2011), it was a very well organised team.
"Now we’re more accustomed to playing at this level, to winning.
"This is one of the strongest teams in Europe and I want to help the team keep winning."
"My relationship with Simeone is spectacular," he continued. "He’s the best coach I’ve worked with in my life and has helped me a lot as a player and as a person.
"The trust he has in me certainly makes a difference in the decisions I make.
"It was great to start with a win (on Sunday).
"It was a very difficult and important game but I got a spectacular reception and was able to make a goal.
"I prepared a lot for this but I have to thank everyone - my teammates, the fans, the board and the trust of my coach. I’m very happy."
