Two second-half goals in as many minutes added the finishing touch to a 3-0 defeat at Roots Hall.
Kevan Hurst opened the scoring for the home side on 28 minutes, getting on the end of an Anthony Straker square ball for simple tap-in at the back post before Ryan Leonard and Barry Corr finished Chesterfield's afternoon through two second-half goals in quick succession.
Marc Richards had an opportunity to pull a goal back for the Spireites from the penalty spot but Daniel Bentley saved the striker's effort brilliantly, consigning Chesterfield to their heaviest defeat of the season.
Less than a minute into the game Sam Morsy set the tone for the afternoon by getting booked for a late challenge on Michael Timlin as the Spireites attempted to settle.
The first real opportunity of the match came for the home side after Luke O'Neill broke down the right wing and lofted a cross towards Corr at the back post but the striker couldn't direct his headed effort on target.
Southend enjoyed the majority of early possession, keeping the ball well amongst themselves but without creating any clear cut opportunities on Tommy Lee's goal.
It was ten minutes before either side forced another attempt on goal, Jimmy Ryan broke from midfield and exchanged a smart one-two with Richards on the edge of the Shrimpers area. The Liverpudlian broke into the box and attempted to direct the chipped through-ball beyond Bentley but he didn't catch his effort well and the goalkeeper smothered the shot.
The home side broke the deadlock just before the 30-minute mark. O'Neill found Straker with a perfect cross-field ball, the winger then took ball down and cut inside of Drew Talbot before squaring for Hurst to tap in at the back post.
Southend had an opportunity to double their lead soon after, Ian Evatt conceded a free-kick on the edge of the Spireites area and received a booking for his troubles. Corr stepped up to take the kick but his effort deflected off the wall and bounced out of play without troubling Lee's goal.
After Chesterfield failed to clear their lines following a Shrimpers corner, the ball fell to Will Atkinson just outside the Spireites box. Atkinson snapped at the shot first time and dragged his effort wide.
As the first half came to a close Jay O'Shea won the ball 25-yards from Bentley's goal, he composed himself before shooting for the far post but his long-range effort just cleared the crossbar.
That was to be the last action of the half as the referee brought the opening 45 minutes to a close with Southend enjoying a slender lead.
Chesterfield started the second half brightly, showing their intent just a minute after the break. O'Shea broke down the right wing before pulling the ball back to Talbot, the full-back crossed into the home side's area but the ball took a deflection and looped into the arms of Bentley before Ollie Banks could get there.
Soon after, Richards found space on the right wing as Luke Prosser lost his footing in defence. The striker broke into the Shrimpers area before cutting back towards Morsy but the ball was cut out and cleared before the midfielder cut direct an effort on target.
Hurst had an opportunity to double his tally for the afternoon on the 55-minute mark. The striker received the ball on the Southend left wing before cutting back into the Chesterfield area and shooting just wide of Lee's goal.
The Shrimpers finally added to their tally just before the hour mark. Leonard exchanged a one-two with Michael Timlin in midfield and was released through on Lee's goal, the Spireites 'keeper charged out of his goal to meet the break but the midfielder smartly lifted the ball over Lee and doubled Southend's lead.
Just moments later, Chesterfield's afternoon went from bad to worse as Corr brought down an Adam Thompson long ball and chipped the ball over an onrushing Lee into the back of the net to the delight of the home support.
The Spireites had an opportunity to pull a goal back after Roberts was brought down inside the Southend area giving the referee no choice but to award a Chesterfield penalty.
Richards stepped up to take the spot-kick and fired it low to Bentley's right hand side but the 'keeper guessed correctly and got down brilliantly to palm the striker's penalty wide.
Bentley was called into action again as Chesterfield chased the game. Dan Gardner pounced on a loose ball and broke into the Southend area before directing a fierce half-volley towards goal but the Shrimpers 'keeper was equal to the effort and magnificently tipped the ball over the crossbar.
The game became stretched as the Spireites pressed and Southend looked to add to their tally. Morsy broke into space outside the Shrimpers area and fired towards goal but his effort was too straight and allowed Bentley to smother comfortably.
As the game came to a close, Roberts had an opportunity to grab a consolation goal. He won the ball outside the area and turned inside of his marker, presenting him with a one-on-one opportunity but the midfielder couldn't get enough purchase on the ball to lift the effort over Bentley and the Shrimpers stopper saved.
This was to be the last action as the referee brought the game to a close. The Spireites will look to put this result behind them as they take on promotion rivals Rochdale at home on Tuesday night.
Southend United: Bentley, Coker, Phillips, Prosser, Timlin (Eastwood 81'), Corr, Straker (Woodrow 74'), Atkinson, Hurst, Leonard, O'Neill (44' Thompson).
Subs not used: Smith, Laird, Clifford, Payne.
Chesterfield: Lee; Talbot, Evatt (c), Cooper, Smith; Ryan, Morsy, O'Shea (Gnanduillet 57'), Banks (63' Gardner), Roberts; Richards (Doyle 74').
Subs not used: Dunbavin, Hird, Humphreys, Brown.
Goals: Southend United (Hurst 28', Leonard 59', Corr 60') 3 - 0 Chesterfield
Attendance: 6,256 (291 Chesterfield)