Following a brawl during their friendly with the Chinese Olympic team, goals from Lee Bradbury, Mark Gower, Efe Sodje and a Kevin Maher brace finished Rangers off.
In a match billed as a six-pointer it was Southend who started more dangerously, with Freddy Eastwood's rising shot flying just over Simon Royce's crossbar after six minutes.
And it was a blunder by the former Shrimpers goalkeeper that put his old club in front.
Skipper Steve Lomas made a routine back-pass to Royce but his clearance cannoned straight off Bradbury and into the net on nine minutes.
The hosts went close to doubling their advantage after 17 minutes following a burst down the right by Jamal Campbell-Ryce.
The winger's cross was punched clear by Royce but fell to Gower who rifled in a right-footed shot that was hacked off the line by Sampsa Timoska.
And Royce did well to turn a Maher free-kick round his left post, before diving to save a Bradbury shot from the edge of the box.
QPR struggled to make much impact up front but should have had a penalty when Peter Clarke's clumsy challenge brought down Lee Cook, but went unpunished by referee Peter Walton.
And Rangers narrowly avoided more red faces in their defence six minutes into the second half when Danny Cullip nearly turned an Eastwood cross into his own net.
But manager John Gregory's half-time team talk had the desired effect as QPR upped the pressure on the Blues goal with a series of corners.
The visitors had their first shot on target in the 62nd minute when Gareth Ainsworth set up Adam Bolder who fired a 25-yard shot straight at Darryl Flahavan.
Eight minutes later the Shrimpers doubled their advantage when skipper Maher chipped a free-kick over the Rangers defence and Gower ran behind to fire past Royce from 14 yards.
Martin Rowlands had a great chance to reduce the arrears on 74 minutes but his 25-yard shot was turned out for a corner by Flahavan.
And 11 minutes from time Southend made sure of the points when Maher's left-wing corner was headed home from close range by Sodje for his first goal of the season.
Martin Rowlands blasted straight at Flahavan in reply before Southend's Alan McCormack's goal was ruled out for offside.
It did not matter as Maher rifled in a snap-shot in injury time and then curled in a free-kick beyond Royce's despairing dive to complete the rout.