Darren Ferguson apologised to supporters for the performance in Doncaster Rovers' defeat at Wycombe Wanderers.
Rovers twice found themselves behind in the first half to strikes from Luke O'Nien, sandwiching an equaliser from Alfie May.
And after the break they struggled to find openings, ultimately suffering back-to-back defeats for the first time this season.
And Ferguson was far from pleased with his side's performance at Adams Park.
"I have to apologise to the fans," Ferguson said.
"We had great numbers here today and to be honest, I wouldn't have been happy watching that.
"I didn't enjoy watching it.
"We didn't look like ourselves which is really disappointing.
"I have to look at why we had a performance like that because it is never going to be acceptable."
Title rivals Plymouth Argyle managed only a goalless draw at Colchester United, ensuring Rovers finished the day with a two point lead at the top of League Two.
And a win for Portsmouth brought them back into the title race, leaving them four points off top spot.
With Rovers missing another opportunity to put one hand on the championship trophy, Ferguson's frustration was tangible.
"I'm extremely disappointed, one with the result, two with the performance," he said.
"Wycombe thoroughly deserved the win.
"To go 43 games with the way we've done it has been excellent.
"I've said to the players that they've had a lot of praise thrown at them.
"And now we can end up stumbling over the line.
"Every point is massive for me. We have to take momentum into next season.
"That's the first time we've had back-to-back defeats.
"But the performance was miles away. It was really disappointing.
"In both boxes we were no where near good enough. We worked on Wycombe, how they played, free kicks, throw ins, second balls.
"They scored from two of them.
"And then some of the decision making in the final third. That is the most important area of the pitch.
"The two boxes are the most important and we were miles away.
"It was a really poor performance."
Goalscorer May was withdrawn in the first half due to a dead leg.
Ferguson confirmed there was no injury for Craig Alcock, who was taken off in the second half for tactical reasons.