Eden Hazard's first-half goal in the Boxing Day fixture was enough to keep the Stamford Bridge club on the pace with their Premier League title rivals.
But Mourinho, who had been moaning earlier in the week about his team not taking their chances, again saw his players waste opportunities in a match in which they had 19 shots.
"It is almost the same story as we had in previous matches - lots of chances, their goalkeeper did very well," Mourinho told Sky Sports.
"We could not kill the game again. When you do not kill the game, you are always feeling the pressure.
"It is a game that if you score the second goal, the picture is completely different and you enjoy the game.
"If you do not score, the team is under pressure when the time goes on and on and you change your mind a little bit instead of going for the second goal."
Next up for Chelsea is Sunday's vital clash with top-of-the-table foes Liverpool but they will be without Ramires after the midfielder picked up a yellow card against Swansea which means he will be suspended at the weekend.
"We lost Ramires with a yellow card, which is obviously a problem for us but it is not a time to cry," said Mourinho.
"It is a time to forget. It means he will have a rest and will be back in a strong condition to play on 1st January."