Palace were never out of the game at Stamford Bridge and started brightly before Fernando Torres gave the hosts the lead.
Marouane Chamakh even had them level before Ramires' strike before the break won it for Chelsea.
Both sides had further chances and Mourinho admits it could have gone either way as his side climbed to second in the table.
"It was tense, it could be four or 5-1 but could also be 2-2," Mourinho told Sky Sports.
"It is tense because you feel the chances you lose, and that you could kill your opponent.
"After that when you don't and when you're not in the best place of your game your opponent can punish you.
"We had a chance to make it 2-0 in the first half through Branislav Ivanovic, we don't and they make it 1-1.
"In the second half when we were winning 2-1 we had lots of chances to score and kill the game, we don't and they do.
"So, four or 5-1 could be 2-2 - we had lots of chances."
Mourinho paid tribute to his counterpart Tony Pulis and said: "At the end of the day it is three very important points against a team that has fantastic spirit and is very well organised according to the ideas Tony wants to bring to his team.
"They were a very difficult opponent to us and difficult to any team."