Truro City assistant manager Dave Newton says he cannot explain how his side threw away 3-2 lead against 10 men to lose 4-3 at Hampton and Richmond.
Charlie Moon gave the hosts the lead after 14 minutes before Andy Watkins equalised after half an hour.
Moon made it 2-1 just after half time before Dean Inman was sent off.
Watkins made it 2-2, and a minute later Les Afful gave City the lead before Moon equalised and Rhys Jones grabbed a winner for the hosts in stoppage time.
"I can't explain it, all I will say is that we're in a relegation dogfight now and we've got to react to it on Tuesday night," Newton told BBC Radio Cornwall.
"Our defending today was shocking, there were no excuses for it and if we defend like that we're going to be in even more trouble," he added.
City have taken just five points from a possible 30 and are five points off the Blue Square Bet South relegation zone ahead of a trip to mid-table Borehamwood on Tuesday.
"We can't sulk, we've got to double our efforts on Tuesday night and respond.
"The most important thing is that we've got to keep working hard, there are games left and points to play for and we've got to keep believing that we'll get out of this and we will do," Newton added.