Kalou, who saw two chances go begging in the first half, one a simple opportunity to score, went on to find the net in both halves as Chelsea strolled to a third straight win in the competition.
Frank Lampard’s first strike in open play this season and an own goal by Luis Perea completed the rout on a pleasing night for Carlo Ancelotti’s side at Stamford Bridge.
“After not playing a couple of games, to come back into the team it was important for me to get confidence back by scoring,” said Kalou.
“All the boys were saying after I missed the first opportunity, ‘Don’t worry about it, it will come’, and I’m happy it came in the end.
“It was very important to win that game because it gave us nine points.”
The win left Chelsea in firm control of Group D. They are eight points ahead of Atletico and three in front of second-placed Porto.
Kalou put Chelsea on the way to victory when he converted a cross from Ashley Cole in the 41st minute.
He added the second six minutes after the restart before Lampard fired home his first goal in 10 games and Perea headed into his own net in the closing seconds.
“It’s good to get confidence back by winning and everyone gave his best today and we have the result in the end,” said Kalou.
“After the disappointment of last week [against Villa] we had the opportunity to show it was a mistake.”
Ancelotti was delighted with Kalou’s performance, which came just weeks after the player signed a new three-year deal with the club.
“Kalou is an important player for us because, when we are without Didier Drogba, he can play and play well,” said the Italian.
“He started the game ‘no good’ because he made a big mistake, but he maintained good motivation and good focus on his match to score twice after that.
“For him, it was very important to score. Also for us. He played very well for us.”
Ancelotti was also pleased with Lampard’s first strike in open play this season. His only goal, barring the one in the Charity Shield, came from the penalty spot against Sunderland.
“I’m happy for Lampard, for sure,” said Ancelotti.
“I think that Lampard is not only important scoring goals. He’s important because he works for 90 minutes on the pitch for the team.
“He’s very generous, an unselfish player, and for me that’s important. Yes, if he scores it’s better, but I want to speak about Lampard for his work, not just for his goals.”
Atletico coach Abel Resino blamed the defeat on his side’s inability to convert their own scoring chances.
Both Diego Forlan and Sergio Aguero were guilty of glaring misses at crucial times.
“It’s one of those bitter tastes,” said Resino. “We probably had as many chances as Chelsea, but the ball just didn’t want to go in the net for us. It’s not going for us. That’s football. My job is to find a solution. You can look to blame someone if you want.”
“I’m not just thinking about the group. I’ve also got to worry about our league form back home. It gets more and more difficult when your confidence is down.
“The boys tried right to the very end. We deserve credit for that.”