The London side slipped from the top of the Premier League after conceding two soft goals from corners against Villa.
"Yesterday we worked on this particular situation," coach Carlo Ancelotti told reporters on Tuesday.
"It's difficult to train for set plays just like it's difficult to train for penalty kicks. But we worked on it because we have to improve.
"You can play a good match but if you don't pay attention once for six seconds you can get a bad result," the Italian added.
Germany captain Michael Ballack, returning to the Chelsea side after missing the Villa game with an ankle injury, said the players had had harsh words for each other this week.
"We have no problem criticising each other in the dressing room," the midfielder said. "With a good team and strong players they have to do this. And we did it. After we shake hands and go back on the training pitch and get on with it."
Ballack said playing well and losing was particularly frustrating.
"It's one of our strengths that we are very well organised so it's a little bit unusual for us to concede two goals in one game," he said.
"It's all about individual mistakes and that happens... You can train (for) many things but if somebody sleeps in a situation you concede a goal so everybody has to be aware of this."
DANGEROUS GAME
Chelsea top Champions League Group D after two victories and Atletico are bottom with just one point.
The Madrid side, who have picked up only six points from their first seven games of the season in La Liga, lost 3-0 to Osasuna on Sunday for their worst top flight start in 15 years.
"It's a very dangerous game because Atletico have not started so well (in Europe) and need points," Ballack said.
"But we are a strong team, we've shown we can reach the semi-finals and we believe in ourselves."
Chelsea have reached the last four of the Champions League in five of the last six years, losing the final in 2008.
Ancelotti also urged caution against Atletico.
"They have very good quality above all in the forward line with (Sergio) Aguero and (Diego) Forlan. We have to pay attention in dangerous areas. Aguero can change a match with his quality," Ancelotti said.
Chelsea will be without in-form front man Didier Drogba, serving the last of a three-match ban for an outburst after last April's semi-final defeat by Barcelona.
Right back Jose Bosingwa, due to return after a two-match penalty, is out with an ankle injury picked up against Villa.
Asked about Chelsea's defensive frailties, Uruguayan Forlan, a former Manchester United striker, said he was expecting nothing but quality in the penalty area.
"They have good power in the air and players who are very strong. Sometimes you make mistakes in football, but it doesn't mean they are going to struggle in that situation."
