Manager Steve Housham felt Gainsborough Trinity "did not show up" in the second half of their 2-1 defeat by Colwyn Bay in Blue Square Bet North.
Trinity led at the break through Leon Mettam's goal but Lee McEvilly levelled before Karl Noon scored the winner.
Housham told BBC Lincolnshire: "I thought they were sloppy in the first 10 minutes but we didn't kill them off.
"I said at half-time 'don't let it come back to haunt us', but we didn't show up in the second half."
Mettam gave Trinity the lead after five minutes following good work from Lewis McMahon, and they had chances to extend their lead through Mettam and Craig Nelthorpe.
Lee McEvilly's header early in the second half drew the hosts level with Noon heading the winner on 72 minutes.
"I don't like criticising my players but I can't back them up," added Housham.
"At half-time there was only one team that could beat us and that was ourselves. We gave the ball away too cheaply and easily.
"The pitch was sticky and heavy but it was the same for both teams, they just wanted it more in the second half than we did.
"The second half was just not good enough."