Failure to solve that problem saw Chelsea fall short in last season's Premier League title bid and Mourinho has targeted an improvement in final-third quality.
Mourinho believes recruits Fabregas and Costa will help overcome that as Chelsea open their league campaign at Burnley on Monday.
The Portuguese boss admitted Chelsea have worked extensively in pre-season on unpicking opponents who set out solely to nullify his side's threats.
"We need more quality in our football," said Mourinho.
"When you have matches with space and time it's much easier to play football. When you don't have space and time because a lot of football is based around tactics and systems: in a very simple way, everything depends on space and time.
"And when you don't have space and time to play, you need more quality.
"We are working exactly in that direction.
"We need more quality in our game, and we are working on that.
"We have worked on exactly that in training, expecting a team to be defensive and try to close every road to goal."
Mourinho's first season in his second managerial tenure at Chelsea ended with no silverware and included defeats such as the galling 1-0 home reverse to relegation-threatened Sunderland.
At the time, Mourinho had to defend his top stars but now he has conceded that only sharper build-up play will allow the west London club to break their trophy deadlock.
He also admitted he will face a big test to keep both goalkeeping rivals Petr Cech and Thibaut Courtois happy as they battle for the first choice number 1 slot - but did not foresee similar issues in the Blues' midfield.
The Chelsea boss believes Fabregas will offer a new dimension in midfield play to complement a host of box-to-box runners.
The former Real Madrid and Inter manager said none of his midfielders will command automatic selection - but neither will any be out in the cold.
"That is not so tough, because we play 60 matches in a season," he said.
"In this first two weeks, it's one match a week, but after that starts the cups, the Champions League and the national team.
"So you have to adapt. Nobody will feel they are first or second choice.
"Mikel, Matic, Ramires, Fabregas, Schurrle, Van Ginkel: so everyone will play, everyone will feel useful, important.
"On the field we have a very good balance."