The night was a personal triumph for Michael Bridges, the pounds 5m summer signing from Sunderland, who scored a well-taken hat-trick in his second game for his new club.
Yet while Bridges was the headline-maker this was a team performance. With the excellence of Lucas Radebe, Jonathan Woodgate and David Batty providing the platform, Leeds' forward talents were able to flourish. It was no surprise to see Harry Kewell among these but those Leeds' fans unfamiliar with Charlton's performances last year will have been equally impressed by Danny Mills at right wing-back.
Given greater scope than on Saturday, when Leeds played a flat back four, he pushed forward to give Leeds the width on the right Kewell provides on the left. The new formation meant Michael Duberry, another summer signing, was given his first start since arriving from Chelsea. Initially uncertain, he looked increasingly solid as the game wore on.
Leeds had been held at home by Derby on opening day while Southampton had unexpectedly won at Coventry but any confidence they had gained from that quickly ebbed away as Leeds made a dominant start.
This owed much to their manager's memory. "We have had one bad performance since I was manager and that was down here," O'Leary said. "I don't like us to be outbattled and that is what happened to us last season. That is not going to happen again and I made them well aware of that beforehand."
Since Southampton rarely lie down at The Dell this made for a physical opening which the referee, Alan Wiley, making his Premiership debut, struggled to cope with. Though he booked nine players, he eventually settled. But by then, as far as Southampton were concerned, the die was cast.
Having booked Matt Le Tissier after a fracas he then gave a harsh free- kick against Chris Marsden after a challenge on Kewell. Harte, who had shamelessly made a meal of Le Tissier's response to his challenge, took it, the ball fell to Bridges and he delicately looped a volley over Paul Jones.
"It was a quality finish," said O'Leary. "He has the potential to be someone. I expect him to make goals and score them."
He certainly did the latter. The second came after 51 minutes, and was an easy finish after Mills had burst down the right past Francis Benali before squaring for the 21-year-old to tap in.
That put the match beyond Southampton who, encouraged by a brilliant save from Paul Jones off Lee Bowyer, had been threatening a comeback. Just before the break Mark Hughes went close with a fierce volley from Le Tissier's corner which struck David Hopkin on the line.
But by the time Bridges scored his third, a neatly flicked header at the near post from Harte's 70th-minute corner, Leeds were rampant and only Jones kept the score down.
In front of him Southampton offered little. "There are lessons to learn from that and we will get stronger and better," said their manager, David Jones.
The next lesson for David O'Leary's young side is at Old Trafford on Saturday. It should be quite a game.
Southampton (4-4-2): P Jones; Dodd, Lundekvam, Richards, Benali; Kachloul (Ripley, 66), Marsden (Oakley, h-t), Hughes, Le Tissier; Ostenstad, Pahars. Substitutes not used: Beresford, Almeida, Moss (g).
Leeds United (3-5-2): Martyn; Duberry, Radebe, Woodgate; Mills, Hopkin (M Jones, 86), Batty, Bowyer, Harte; Bridges, Kewell (Bakke 82). Substitutes not used: Haaland, Robinson (gk), Hiden.
Referee: A Wiley (Staffs).Reuse content