Mourinho's poor record at St James' Park – he has collected just two points in his four trips to the venue – continued as Yoan Gouffran and Loic Remy scored in the final 25 minutes to hand Newcastle the points.
That was after Chelsea had controlled the first half, in which John Terry hit the crossbar and had a header cleared off the line.
After the match, Mourinho questioned the fight of his players and admitted that they deserved to lose as they missed out on the chance to move to the top of the Premier League table.
"We were too soft with the ball and too soft without the ball," Mourinho said.
"We were not aggressive enough in possession. We deserved to lose. I'm not sure if Newcastle deserved to win, but we definitely deserved to lose.
"I feel like I picked 11 wrong players. Of course I'm exaggerating but I always have this feeling when I lose.
"We gave them 45 minutes of a friendly in the first half and we only had a reaction after they scored the first goal."
The defeat – Chelsea's second of the Premier League season – came after they failed to convert their dominance in the first half into goals.
"The game was quite easy to play in the first half. We had lots of space. We were not sharp. We were not intense with the ball," Mourinho told BT Sport.
"We defended quite well. Our back four did a simple, easy job. But we were not aggressive with the ball and we let the game go, waiting for a chance to score a goal or a chance for them to score a goal and lose it."
The Portuguese insisted, though, that the result would not prove defining in the title race, with plenty of time to recover.
"The title race is there for everybody. It is open for everybody," he added.
"If Arsenal wins today (against Liverpool) and they open the gap…for us and for Liverpool, they just open the gap, it is not definitive."
