Southend manager Phil Brown felt his team were out-fought by Northampton as the Cobblers continued their resurgence with a 2-1 win.
Northampton made it back-to-back victories with a goal in each half from Mathias Doumbe and Chris Hackett.
Michael Timlin netted inbetween to bring the Shrimpers level but they were eventually defeated by a side fighting for their lives at the foot of the Sky Bet League Two table.
Brown wants the Blues to play with the same kind of spirit as they aim to keep their promotion hopes alive.
"I thought in the first half it was a good old-fashioned game of football between two committed sides," said Brown, whose side are now without a win in eight games.
"The battling qualities of the players was there for all to see but it was disappointing to concede from a set-piece and words were said at half-time.
"Quite simply we didn't match them in the battle in the second half and that was the difference between the two teams.
"Northampton fully deserved to win the game - they looked like they were fighting for their lives and we've got to start fighting like that ourselves.
"We need that mentality between now and the end of the season. Regardless of where you are in the division, we've got to fight like they fought - like our lives depend on it."