Beattie swept in for his ninth goal in seven matches, converting a pinpoint cross by substitute Brett Ormerod, to reward Southampton for a good late fightback after West Ham had controlled the first hour.
The result left West Ham rooted to the foot of the premier league and still without a home win all season -- with the pressure mounting on Roeder.
Southampton, who beat champions Arsenal last week, remain 10th after only their second win in nine attempts at Upton Park.
They arrived at the east London ground only 30 minutes before kick off on Monday because of traffic congestion and they looked to be still on the bus in the first half as West Ham totally dominated.
Jermain Defoe had the first clear chance after nine minutes, hooking a volley wide when left unmarked six metres out, while Trevor Sinclair was off target with a header five minutes later.
The best chance of the half came in the 35th minute when defender Ian Pearce, playing up front in place of the injured Freddie Kanoute, struck a firm shot goalwards but saw it well saved by Finnish goalkeeper Antti Niemi.
Southampton came to life only in the last five minutes of the first half as Beattie headed wide and Rory Delap forced David James to make his first save of the night.
West Ham made all the early running again after the break, with Paolo
Defoe dragged a shot wide after an hour then forced Niemi into another save minutes later.
Southampton finally dragged themselves into the match and Beattie was furious when the referee waved play-on after he had been blatantly blocked by Czech defender Tomas Repka as he advanced on goal 10 minutes from time.
Delap then almost embarrassed James, catching him in possession, only for the England goalkeeper to make a scrambling recovery.
POSITIVE MOVE
West Ham were looking tired and a ragged and Gordon Strachan was rewarded for his positive move in sending on Ormerod when the former Blackpool striker picked out Beattie for the winner.
Strachan was delighted with the win, though somewhat relieved.
"For an hour they were the better team. We went out and looked like we weren't ready for the sort of "cup tie" football we needed to win here," he said.
"But we played much better in the last half hour and I thought Brett (Ormerod) was excellent."
Beattie added: "I think we got what we deserved for our second half efforts.
"But West Ham have got quality players in the side and I'm sure they'll get out of it."
The home fans, not so certain of an early escape, demonstrated afterwards against chairman Terrence Brown, though Roeder is the more likely man in the firing line.
