Danny Wilson could not hide his anger after Sheffield United conceded a late equaliser to draw 1-1 at Colchester.
The Blades appeared to be cruising to victory, following John Cofie's superb 17th-minute opener. But former Sheffield Wednesday striker Clinton Morrison grabbed a point for the U's with 17 minutes to go.
Blades boss Wilson said: "I'm more than frustrated - I'm very annoyed. The game was there to be won for us.
"I'll take nothing away from Colchester, but we've created enough chances to win a host of games. But we didn't convert those chances and we weren't clinical enough in front of goal.
"And then to concede like we did with such a sloppy goal when there was nothing at all on in their favour apart from a corner was very disappointing.
"It's a real wake-up call for one or two players because I wasn't happy with some of the performances.
U's boss John Ward said: "It was a bit of a scrappy draw, but it's better than a scrappy defeat. The way that the point was obtained means that it was the best one of the three that we've earned so far this season. "We had to stay with the game and our goalkeeper again has had another very good game. If we hadn't stayed with it, we would have rolled over and lost the game.
"When Sheffield United have the players they have got, it's sometimes hard to stay with them. But if you go away from it and accept that they're better than you, you'll get beaten.
Sheffield United dominated for long periods and Matt Heath cleared Stephen Hunt's effort from underneath his own crossbar. But the visitors were ahead in the 17th minute through Cofie, who fired a looping 25-yard shot over goalkeeper Mark Cousins.
Colchester equalised when Morrison converted from close-range after Magnus Okuonghae had helped on Anthony Wordsworth's corner. Substitute Andy Bond struck the post late on and Cousins tipped McMahon's header on to the crossbar as the spoils were shared.