His 20 goals helped a brilliant Blues side to league glory in 2015, but captain John Terry knew they were destined for glory from the beginning.
Costa had a notoriously short temper and often got into scraps with his opponents on the pitch, but not many, however, would have predicted him to fight one of the club's much-loved member of staff Billy 'Rocky' McCulloch.
But that's what happened, as Terry recalled a 'boxing match' between the pair that had everyone in stitches during a pre-season tour in 2014.
Sharing the clip on Twitter, he wrote: "After this I knew we would win the league. What a Legend. I'm crying watching this."
Costa can be seen scrapping McCulloch before he brings him to the floor and ends the play fight to howls of laughter from the squad.
In the Twitter thread, Terry, who is one of Chelsea's best ever players with five Premier League titles and a Champions League crown to his name, was asked what he thought of Costa as a teammate.
The former England captain was full of praise for the striker.
He replied: "Genuinely a top guy. I loved him because he gave everything, every single day for our club. He cared and was an unbelievable player."
Costa was a cold-blooded killer in front of goal for Chelsea and also played a big role in a Carabao Cup victory, netting the second in League Cup victory over Spurs at Wembley in 2015.
However, he left Chelsea after falling out with Antonio Conte in 2017 and headed back to Atletico Madrid, before joining Athletic Mineiro last summer.
But he has a special place in the hearts of everyone connected with Chelsea owing to his 59 goals in 120 appearances.