The 25-year old will likely make his Stamford Bridge debut tonight, as Jose Mourinho's men challenge Real Sociedad in their last pre-season friendly before the Premier League begins this weekend.
Having already scored two fine goals in his non-competitive spell with the Blues, the Brazil-born Spanish international is on the path to forgiveness - having been instrumental in Atletico Madrid knocking the West London club out of last seasons Champions League.
And Costa is keen to having the backing of the Chelsea fans, apologising for his goalscoring exploits last season.
Speaking to the Evening Standard, Costa expressed his admiration for the Blues fans, who never gave up on their team in the crucial Champions League game.
The striker said: “Now I can say I’m really sorry for the part I played in the game we won at Stamford Bridge.
"I remember the atmosphere and the passion of the supporters. They stayed right until the end, getting behind their team, even though it was unlikely they could win after we scored two quick goals. I liked that."
Whilst words may be enough to calm one storm, Costa is relying upon his footballing talent to cement himself as a key player as Jose Mourinho's men look for Premier League and European success.
“I hope my actions on the pitch and my feet will do the talking and then people can decide if I’m a good player or not, if I’m improving or not. All I can say is I love playing hard and fairly.
“I love playing at a high intensity and, hopefully, that can rub off on some of our players. I just want to become better and, hopefully, I can do that here.
The striker was part of the Spain squad that crashed out of the World Cup this summer, although a late season injury resulted in Costa struggling to find fitness and form at the Brazil-based tournament. Despite his collapse on the world stage, the 36-goal man is confident that he can improve - having joined one of the best clubs in the world.
“I want to improve, not only as a player but as an individual, and I believe this is the perfect place for me to do that. That’s the reason I chose Chelsea and why I want to defend this shirt.
If Costa can find his scoring boots once again, there is no doubt that Chelsea will be fighting for every trophy come the close of the season.
And for the Blues fans, they will just be thankful that the Spaniard is keeping them in competitions this season - rather than knocking them out of them.
Will Diego Costa bring Chelsea silverware this season?