Swindon manager Paolo Di Canio accused his players of lacking desire as they were beaten 1-0 by resurgent Colchester at the County Ground.
Former Robins defender Michael Rose's drilled 70th-minute free-kick was enough to earn Colchester's new manager Joe Dunne his second win from as many matches in charge.
Di Canio said: "This is the first time I have not been angry after a game but I am not surprised and we will be in training on Wednesday. Enthusiasm, passion and desire is more important than the system I play.
"I said at half-time 'defend and we can get a draw' but we had no passion or desire. We learnt from this game and to get the way I want the team to play we will have to work hard."
Rose played 41 games for Swindon during the 2010-11 season but the ex-Manchester United trainee showed no mercy on his former club, beating goalkeeper Wes Foderingham with a well-placed low shot.
Both sides struggled to create chances and contrived to produce a less than entertaining game. Swindon striker Andy Williams threatened an early goal when his eighth minute shot on the turn was smothered by Colchester goalkeeper Mark Cousins.
At the other end U's midfielder Anthony Wordsworth sent a shot just over the home crossbar. Cousins - playing with a broken finger - was rarely tested and Jamie Collins, Williams and Matt Ritchie all failed to hit the target for Di Canio's side with presentable second-half openings.
Substitute Freddie Sears almost added to Colchester tally late on after seizing on a defensive error but could only drag his shot wide.
For Colchester boss Dunne the honeymoon period continues. He said: "To a man we were great but we have to keep building and find ways of combating opponents' tactics. We have to learn what we can and cannot do but the players performed to the maximum. My challenge is to make them better players."
Dunne added: "Swindon are a magnificent side, which can be driven by their manager into the Championship, but we deserved to win and we edged it.''