Mark Yates apologised to Cheltenham supporters for what he admitted was an unacceptable performance against Accrington.
Stanley ended a four-match winless run to edge clear of the relegation zone in League Two with first-half goals from George Bowerman and Luke Joyce, before Jamie Cureton pulled one back for the Robins after the break.
Yates said: "We should have got something out of the game with the chances we had in the second half, but you can't play like we did in the first half against anyone and expect to get a result.
"One or two of my players looked lethargic and it's not good enough. We have conceded two sloppy goals, but in the second half we had a go.
"But the first-half performance has cost us three points and it's another home defeat which hurts me, hurts my staff and I hope it hurts the players somewhere near as much as well.
"I apologise to the supporters for the first half and the players don't come out with any credit in the second half just for having a go, that doesn't cut the mustard and we have to be at it from the start.
"We warned them it would be hard, but we were poor in the first half and it has cost us."