Abdul Osman was sent off at the start of the second half against Port Vale last weekend but Town held on for a goalless draw.
However, after Leon McKenzie had put them in front at Underhill, Liam Davis was dismissed in the ninth minute and Sampson`s side went on to lose 4-1.
"We've never been out of the relegation battle," said Sampson. "We need to stand up and be counted, improve our discipline and try and keep 11 men on the pitch. If we can do that it will help us get away from this position. But if we keep doing what we did here then we'll be in the relegation battle all season.
"I thought we had got near to turning the corner but we have had a setback and we have to start again. You can't keep doing it with 10 men. We did it last week and held out for 45 minutes but that's not going to happen every week and we suffered the consequences here."
Sampson added: "We'll dust ourselves down and move onto the Rotherham game where we'll hopefully get a good result. We're in the predicament we are and we have got to keep battling out of it."
Source: PA
Source: PA