Paul Cook believes Southend will be firmly in the promotion mix come May after Chesterfield were on the end of a 3-0 defeat.
Goals from Kevan Hurst, Ryan Leonard and Barry Corr saw the in-form Shrimpers come out on top in the battle between the top-five rivals in League Two.
"This was always going to be difficult but credit to Southend, they're a very powerful side and you know they will be in the shake-up come the end of the season," said Cook.
"I thought going forward we stuck at it and created chances but that's not enough.
"One slip up by Drew Talbot has cost us with the first goal, especially when a team are at home they get in the ascendency and the crowd get behind them.
"But the main thing now is we look to Tuesday against another team around us, with Rochdale coming up, and focus on picking ourselves up and getting a result."