The Nigerian's sloppy attempted pass was a mistake that contributed to the Italian side's late equaliser after the Champions League holders had earlier been two goals up
Last season's winners started their defence well, going 2-0 up with quickfire goals from Brazilian youngster Oscar, but Arturo Vidal’s swift reply was consolidated by a Fabio Quagliarella strike late on.
Mikel gave the ball away in the build-up to the equaliser and he told Sky Sports after the game: "I think we switched off. It was a pass to Eden [Hazard] that didn't quite get there and then we just switched off.
"We should have dealt with it properly."
The Nigerian had been encouraged, however, by their energetic beginning to the match, adding: "I think we started the game well, we scored two goals and we had more possession of the game. We had the game under control but they scored one goal.
"We came out in the second half trying to do something in the way that we started the first-half but their second goal was a cheap goal to give away."