Matic dismissed the idea that his side underestimated the Black Cats ahead of their Champions League semi-final clash against Atletico Madrid and instead put the defeat down to bad luck.
"We are always focused. For us, the next game is the most important," Matic told Chelsea's official website.
"Sunderland was the most important game, we spoke about that before it.
"This is football and sometimes you have to lose. We did give our best but we were unlucky and we lost because of that."
The 25-year-old Serbia international rejoined Chelsea from Benfica in January.