Substitute Alan Smith's goal clinched Leeds' win
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Leeds United, who finished so strongly in the Premiership last season, got off to the perfect start this time round thanks to second half goals from Lee Bowyer and Alan Smith.
The game changed completely just past the hour when David O'Leary revamped his lacklustre side, bringing on Eirik Bakke and Smith in place of David Batty and Robbie Keane.
The crucial first goal came soon after the changes.
An Ian Harte corner was headed back by Rio Ferdinand to Bowyer on the edge of the box and the Leeds midfielder let fly with a volley which flew past the Southampton goalkeeper Paul Jones.
Then the youthful Smith intervened, scoring a wonderful solo goal to make the game safe for Leeds in the 79th minute.
Fabulous save
Until Bowyer's strike, Southampton had coped comfortably with Leeds' attacks, with captain Dean Richards superb.
The visitors had the edge in the game's opening half and Nigel Martyn was in superb form in the Leeds goal.
Martyn's most important intervention came just after the restart when Ferdinand
slipped and the ball broke loose for Uwe Rosler.
The German striker found himself in oceans of space - but Martyn spread himself wide to his right to made a fabulous save which kept his side in the game.
Leeds had begun the more brightly of the two sides with Keane, preferred ahead of Smith to partner Mark Viduka in attack, menacing as Elland Road was deluged by heavy rain.
Southampton fought back and twice Kevin Davies brought good saves byl Martyn.
The England international goalkeeper, who had a torrid time in the midweek friendly against Holland, proceeded to thwart Chris Marsden, Marian Pahars and Southampton debutant Anders Svensson.
Bowyer spurned Leeds' best chance of the opening period when the ball stuck under his feet after he had been released by Olivier Dacourt.
That was the cue for Leeds' Australians to take centre stage as first Viduka powered a flying header from a corner just over the Southampton bar.
Then winger Harry Kewell, back to full fitness after last season's prolonged injury lay-off, swept past several defenders only to drag his shot across the face of the goal.
Southampton's committed approach saw both Davies and Chris Marsden yellow-carded by referee Clive Wilkes.
And late in the game, as the visitors' frustration increased, Klaus Lundekvam was dismissed for a late tackle on Kewell.
Leeds United : Martyn, Mills, Ferdinand, Matteo, Harte, Bowyer, Dacourt, Batty, Kewell, Keane, Viduka. Subs: Kelly, Woodgate, Smith, Bakke, Milosevic.
Southampton : Jones, Delap, Lundekvam, Richards, Bridge, Davies, Oakley, Marsden, Svensson, Rosler, Pahars. Subs: Moss, Beattie, Benali, El Khalej, Tessem.
Referee: C Wilkes (Gloucester).