The Spanish duo have made a big impact since moving to Stamford Bridge ahead of the 2014-15 campaign, with Fabregas leading the league for assists, while Costa jointly leads the goal-scoring in the Premier League.
The Belgian told The Express: "The time it takes to develop a relationship on the pitch depends on the guy. Sometimes it's quick, sometimes not. But it's easy for me to play with them because they understand football and are very good players.
"We didn't need to train two years together, just one week was enough. They know when I move and I know when Costa and Fabregas move. It's a pleasure to play with them."
Chelsea will look to continue their unbeaten start to the Premier League season when they host Queens Park Rangers tomorrow.