Conte and Costa's sole season together was disrupted by a training-ground row before they got on the same page long enough to deliver the title.
The France global was played in by Filipe Luis before firing across Rico to settle the argument and leave Atletico with two wins from two in their new stadium.
Despite starring for Conte last season in the Premier League, Conte binned the striker after outlining his plans over the summer.
In any case, the change had the desired effect as Chelsea kept a clean sheet, running out 4-0 winners courtesy of a hat-trick from Alvaro Morata and a strike from Pedro.
Sunday was Chelsea's first hat-trick since Costa netted three times against Swansea City at the start of the 2014/15 season, with the departing Spaniard arguably not quite showing the finishing touch of a truly world-class centre-forward during his Stamford Bridge career.
Atletico Madrid defender Filipe Luis has said he is "proud of this club" for bringing striker Diego Costa back from Chelsea.
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Diego Costa insists he was "very happy" at Chelsea but is thrilled to be coming "home" to play for Atletico Madrid.
The frontman scored 59 goals in all competitions for the Blues, but missed 12 games through suspension and in December 2015 was labelled the "most hated footballer" by French newspaper L'Equipe. "Last season they were beaten by Real Madrid [in the semi-finals]".
"I think we are managing him very well".
Asked what exactly he meant by "polite", Conte, a strict disciplinarian, a man schooled in the organised ways of Italian football, explained: "He's a really good guy".
"We have had a tricky start in terms of fixtures but I think we have done okay".
"Each time I would pass the ball to him it would nearly be a goal, and that is why I'm delighted like everyone in the team".
"I repeat now: I'm not interested to talk about the past", Conte said.