Mourinho has repeatedly insisted this season that his players must learn to perform when the results really matter, unlike in the last two campaigns when Chelsea finished 25 and 14 points adrift of the Premier League champions, respectively.
Yet the 1-0 reverse at Selhurst Park, against a side fighting relegation, appears to have blunted the Blues' title aspirations, with Mourinho responding to the defeat by ruling his team out of the race.
With Liverpool now top by two points and Manchester City two points back in third place but with two games in hand, Chelsea's fate is certainly now well out of their hands.
Mourinho has previously stated his wish to sign one or two players this summer to bolster his squad, with a goalscoring striker the priority in the wake of limited returns from Fernando Torres, Samuel Eto'o and Demba Ba this season.
Diego Costa of Atletico Madrid has long been linked with a move to Stamford Bridge, as have numerous others, and while Mourinho knows he must continue to develop the existing talent in the squad, he concedes new faces are inevitable.
"It's clear in everybody that Chelsea next year wants to bring a striker," said Mourinho, while remaining tight-lipped on the futures of Torres, Eto'o and Ba.
"It's also clear that we want to improve our players. I can't and I don't need to improve (Branislav) Ivanovic, (Gary) Cahill, John Terry.
"There are other guys I need to improve. I think we are doing that step by step, but it's not enough to be champions."
He suggested some Chelsea players were out of their comfort zone at Selhurst Park, just as they had been in losses at Everton, Newcastle and Stoke earlier in the season.
"The easiest thing to do is to play well, is to perform, when you are not playing for something big," Mourinho said.
"The difficult thing is to perform when you feel the heat. Because of that some (players) are big and some are not so big.
"I don't think it's courage. I think it's personality qualities.
"You have players for everything and you have other players that are in their habitat in some circumstances."