Swindon manager Richie Wellens shouldered the blame after his high-flyers were thrashed 3-0 at home by mid-table Colchester.
Theo Robinson scored twice to bring his old club’s three-match winning streak to a shuddering halt.
Wellens said: “For the first half an hour, we were very good, and then Mathieu Baudry goes off injured and the whole dynamic of the game changed, and that is my fault.
“I will take that on the chin because I probably made the wrong substitution, I will learn from that.
“We made a few chances but without really playing fluently.
“We have come away from what we have been doing. Credit to them, they have won 3-0 without really doing much.
“They scored one from a set play and caught us on the counter-attack twice – I’m disappointed with myself tonight.
“A few players went off the cuff and did what they wanted to. We came away from what we’ve been doing.
“But credit to Colchester, the first goal was a copy of their first in the Carabao Cup and then they caught us out on the counter-attack twice.
Swindon dictated play in the first half but failed to properly test U’s goalkeeper Dean Gerken, with Eoin Doyle’s rifled shot wide being their best chance.
Colchester opened the scoring against the run of play when Tom Eastman headed in a Cohen Bramall corner during first-half stoppage time.
Robinson made it 2-0 from Brendan Sarpong-Wiredu’s cross, but Colchester had home goalkeeper Luke McCormick to thank by letting the ball squirm through him.
It was all over when Robinson added his second and Swindon’s third in the 75th minute with a powerful effort into the top corner after Frank Nouble led a quick break away.
The win moves Colchester up to 13th in the League Two table.
U’s manager John McGreal said: “I’m delighted with the whole performance.
“I do firmly believe that Swindon will be in and around it this season because of some of the football they’ve applied themselves has been fantastic.
“I’m delighted that we improved on Saturday’s performance and come away with a win.
“The first goal gives you a shot in the arm. I think we grew into the first half.
“We haven’t scored as many goals as we would have liked. We made five changes to Saturday’s team and the boys that have come in have been champing at the bit, it was a great performance.”