Real conceded after only two minutes at the Sanchez Pizjuan when Piotr Trochowski volleyed in unmarked at a corner, and they were outfought in a bruising encounter that left them with four points from their first four games.
"I am only worried about my team," Mourinho told a news conference when asked about the points gap on their arch-rivals Barca, who won 4-1 at Getafe earlier in the day to maintain their 100 percent record.
"I am worried that since the season started officially we have only really played well in the Spanish Super Cup. Nowhere else. More than the points I am worried that in this moment I don't have a team.
"Congratulations to Sevilla, they deserved to win without any doubt. We got the prize we deserved considering how badly we played."
Madrid opened their campaign with a 1-1 draw at home to Valencia, were shock 2-1 losers at Getafe and after beating Barca to lift the Spanish Super Cup, strolled to a 3-0 win at home to Granada.
The Granada win, however, just before the two-week break for internationals, saw Cristiano Ronaldo hit the headlines.
The world's most expensive player told reporters after the game, when he failed to celebrate scoring two goals, that he was 'sad', for 'professional reasons' and that the club knew why.
With no official comment from the Real hierarchy, local media has been full of speculation that Ronaldo was seeking a better contract, that he wanted to leave, or that he did not feel he earned the respect of his team-mates and the fans he felt he deserved.
"It's got nothing to do with the rumour of the last two weeks," Mourinho said when asked if the Ronaldo situation had unsettled his team.
"I don't think today was any different to the games we played against Getafe or Granada. To me, it's to do with the collective spirit.
"There are very few heads who are committed and concentrated, and who have football as the priority in their lives. When you don't have people who are committed, it's tough.
"But I am the coach, and if there are people who aren't committed it is my fault."
Mourinho's controlled and measured outburst against his players comes after a similar attack following their defeat at Getafe.
"At the break, I changed two players but I wanted to change seven," he added.
"The image of my team at this moment is a team without concentration, without the willingness to compete. When you compare Real with Sevilla it is easy to understand.
"For Sevilla, every ball was the last one in their life. They played with perfect aggression in everything. They wanted to play quickly, move the ball quickly.
"My team did it against Barcelona, and haven't done it in any other game."