Two goals in the first 7 minutes saw promotion chasing Doncaster Rovers move up to second place in the table.
Leo Fortune-West and Michael McIndoe got the goals to leave Southend in the bottom three and only 3 points away from the relegation zone.
Doncaster chairman John Ryan this week stated that he wanted Rovers to be in the first division by the 2005 season and his side looked a different class to struggling Southend.
United, who missed out on a lucrative FA Cup tie against Premiership Chelsea when they lost at Scarborough in midweek, made a dreadful start to this match.
Rovers went 2-0 up in the first seven minutes and the game was effectively over.
Leo Fortune-West, who had gained promotion six times in his career, scored Doncaster's first when he was unmarked and easily headed passed Darryl Flahavan after three minutes.
The Yorkshire club doubled their advantage with their next effort as Michael McIndoe tapped the ball home following a cross from Gregg Blundell.
Doncaster, who thumped Leyton Orient 5-0 last week, realised their three points were in the bag and dropped and let Southend attack them.
Despite having a lot of possession United created little and only tested Doncaster goalkeeper Andy Warrington twice when he stopped a Tes Bramble header and later blocked a Leon Cort effort.
Doncaster assistant manager Micky Walker said: "It was one of those games where we started very brightly and we were impressive in the first few minutes.
"In the second half they pressed us but we decided to defend because 2-0 was good enough and we are very happy with the result." Southend have now lost 9 games at home, the worst record in a division and unless that changes quickly will be playing Conference football next season.
If Doncaster continue playing in this fashion then it is likely they will win promotion for the second successive season and should be playing 2nd division football next season.