Six years to the day since his most recent Champions League match as Chelsea boss, a draw with Rosenberg which marked the end of his first spell in charge, Mourinho's men followed up defeat at Everton by falling victim to the Swiss side's first win in England at the 11th attempt.
Goals from Mohamed Salah and Marco Streller, after Oscar had put Chelsea in front, also saw Basle end the Blues' 13-match unbeaten run at home in European competition.
Next on October 1 Chelsea play at Steaua Bucharest, who beat them in Romania earlier this year, before two matches with Schalke, as the 2012 European champions bid to avoid a second successive season featuring a premature end to their Champions League campaign.
"When we lose, I am the responsible (one)," said Mourinho, who did not see onlooking Chelsea owner Roman Abramovich in the immediate aftermath of the defeat.
"We lost three points that we must get somewhere. We must get them, (in) Basle, or Schalke, or Bucharest, or all of them or some of them.
"Normally you have to win the matches at home and get a few points away.
"Now we must win six points at home, Schalke and Steaua, but we have also to win points away. Probably we have to go to win at Basle to compensate for the defeat today.
"But the objective of finishing in the top two in the group phase and to go to the next stage of the Champions League is an objective that is not lost, far from it.
"It's an objective we're going to fight for and it's an objective that I believe very, very much that we're going to achieve."
Source: PA
Source: PA