Poor defending costs Robins dear.
Cheltenham Town were consigned to their second successive home defeat, this time by in-form Southend United.
It had all looked so promising as half-time approached after Jermaine McGlashan's second goal of the season had given Mark Yates' side a deserved lead.
But their challenge unravelled within eight minutes of play following a passage of sloppy defending that had gifted the Essex side an advantage they never looked likely to surrender.
Sean Clohessy levelled the match a minute before the break to change the complexion of this match but despite the manager's half-time briefing, they found themselves two goals adrift with 52 minutes on the clock.
Yates' side will get the opportunity to put things right on Tuesday night when Oxford United visit - they too were heavily defeated today - but there will need to be a marked improvement at the back if they are to give themselves the best possible chance to beat their local rivals.
Yates kept faith with the side that came away from Wycombe Wanderers' Adams Park ground with a point last weekend, deploying the 4-2-3-1 formation which worked so well against the Chairboys that afternoon.
There was no change on the bench, although striker Chris Zebroski was left out of the squad as a precautionary measure through sickness, while Danny Andrew joined Cambridge United on loan two days ago.
The Shrimpers were also unchanged from the side that registered their third consecutive win against Dagenham and Redbridge seven days ago.
The home side carried on where they left off in Wycombe, starting the game in fine fashion and took the lead with a quarter of an hour played.
Scott Brown had been called into the first save of the match to deny Britt Assombalonga when he outjumped Steve Elliott to meet a ball from the left with a firm header.
But the goalkeeper turned defence into attack with a searching ball down the left, where Sam Deering picked up play.
The former Barnet man beat his marker and sent over a low ball and McGlashan did the rest from 12 yards, despite skipper Chris Barker's desperate effort to cldear his line.
The lead was more than merited after a period of incisive passing and movement which had caused the visitors a number of problems in the opening exchanges.
Moments later Shaun Harrad, and then Darren Carter drew a smart double save from goalkeeper Paul Smith before Marlon Pack tested the Southend number one from distance.
Pack was then involved in one of the most extraordinary chances ever seen at Whaddon Road mid-way through the first half, which came about when he smashed a ball under pressure from Kevan Hurst near the half-way line.
The ball flew towards the unguarded Cheltenham goal, but fortunately from Scott Brown's perspective, it dropped inches over the bar.
The midfielder was involved again three minutes later, arrowing a 30-yard free-kick a foot the wrong side of the left upright.
Next Kaid Mohamed released one from similar distance, but this time Smith flew to his left to turn it around for a corner which came to nothing.
There was a half-chance for Keith Lowe, but it was Southend that finished the half the stronger and pulled level a minute before the break Sean Clohessy.
Assombalonga had caused Lowe problems through the opening 45 minutes and jinked past the defender only to see his angled shot pushed onto the post by Brown in the build-up.
Lowe then immediately made amends to clear Tomlin's dangerous low ball.
But as played unfolded down the right, Hurst pulled one back into the path of the Southend right back, who beat Brown with a low drive from the edge of the box.
The Shrimpers had created a two-goal cushion within seven minutes of the restart, claiming both their goals from set pieces to put paid to Yates' half-time briefing.
First Dave Martin supplied the ball from the right, finding Cresswell who brought a save from Brown with a glancing header. Brown parried it onto the left post, but Assombalonga pounced to head home from close range.
Then Martin aimed one towards Mark Phillips from the left, who rose highest to place the ball beyond Brown to send the 276 travelling fans into noisy celebration.
Cheltenham were wobbling, and Hurst should have made it four only three minutes later but he stabbed his effort wide in a great position inside the box.
Every time a ball was sent into the Cheltenham box, Southend looked likely to benefit.
Next Cresswell was denied by his own player, Tomlin, when he met another ball with a firm header, on this occasion a corner from Hurst out on the left.
Brown dived to his right to prevent Assombalonga's drive finding the net, then the striker missed the target after connecting with another menacing ball by Hurst.
Yates sent on Darryl Duffy (for Mohamed), Russ Penn (Deering) and Jeff Goulding (McGlashan) to rescue the game, and Cheltenham rallied.
The best chance fell to Harrad but Barker slid in to clear the danger. Goulding's back-heeled drew an instinctive save from Smith, but in the end Cheltenham were left to rue the poor defending at the start of the half for defeat here.
CHELTENHAM TOWN: Brown; Jombati, Lowe, Elliott, Jones; Pack (c), Carter; McGlashan (Goulding 81), Deering (Penn 77), Mohamed (Duffy 75); Harrad. Subs not used: Hooman, Roberts (Gk), Graham.
SOUTHEND UNITED: Smith; Clohessy, Phillips, Cresswell, Barker (c); Hurst, Spicer, Timlin, Martin (Straker 87); Tomlin, Assombalonga. Subs not used: Benyon, Woodward, Njie, Belford (Gk).
REFEREE: Scott Duncan
ATTENDANCE: 2,751 (276 from Southend)