John Terry's own goal proved decisive at Selhurst Park as the Blues suffered a second surprise defeat in the space of a fortnight, having previously gone down to Aston Villa.
Chelsea's latest loss left them just three points clear of Manchester City, having played three more games, while Liverpool could also climb above them with a win over Tottenham Hotspur on Sunday.
Mourinho maintains that the Blues will keep fighting until the end, but he does not believe their rivals will slip up.
"I think it is now impossible to win the title. We depend too much on other results," Mourinho told Sky Sports.
"With what happened two weekends ago (losing to Villa) and today, it is too much now and we depend on too many results.
"Of course, with my mentality, I want to try and win every game.
"The main objective is to finish in the top four. The second objective is to finish in the top three, which is also important.
"Since the beginning of the season I am just trying to win without thinking too much about positions, and about points."
Mourinho absolved his defenders - Branislav Ivanovic, Gary Cahill, Terry and Cesar Azpilicueta - of blame for Saturday's loss, but was not shy at pointing fingers at others.
He said: "My four defenders, phenomenal performance, as always. The others I'd prefer not to analyse individually.
"We missed some qualities. Mentality and a little bit of quality. Mentality because the opponents beat us clearly on that. Strong mentality, aggressive, committed.
"Every one of them played, I think, at the top of their potential and that, in football, is important.
"Clearly we have some players, because of their profile, who find it difficult to perform in some profile of matches.
"You have Ivanovic, Terry, Cahill and Azpilicueta and they perform in the sun, in the rain, small pitches, big pitches, aggressive teams, non-aggressive teams, possession teams, not possession teams and they perform every game from day one to the last day.
"And you have other players who are fantastic in some matches and disappear in other matches."
For Mourinho, the disappearing acts have happened in four of Chelsea's five losses this season, all of which have come away from home.
The exception was the defeat at Aston Villa when the Blues boss was unhappy with referee Chris Foy's performance.
Mourinho claims he was trying to avoid an incident similar to when Eden Hazard was sent-off for kicking a ball-boy at Swansea last season when he approached one of Palace's ball-boys in stoppage time.
The Chelsea boss suggested the boy had been told to return the ball slowly.
Mourinho said: "The kids were doing that all the time, so I went to stop Azpi and I had the chance to get the kid, and the kid was cute.
"He came to me and I told him if he does this, 'one day somebody will punch you'.
"But the kids, it's not their fault. It was not me, for sure (telling the kids to slow it down). I was losing."