On the positive side, the performance of Louis Saha served notice that the long search for a partner for Ruud van Nistelrooy up front has ended in success.
The 25-year-old Frenchman, signed for Â£12.8million from Fulham last week, produced a superb all-round display.
A goal, all be it coming from a massive deflection off Southampton striker Kevin Phillips, came along with a series of skilful and delightful touches.
He tackled back on numerous occasions and his pace caused problems to Southampton's defenders on the heavy Old Trafford pitch, made worse by incessant rain.
Saha left to a standing ovation in the 70th minute, but the Frenchman's role was only one more part of this amazing game.
Southampton made clear from the start that soaking up the pressure and holding United was no part of their plan.
In the fourth minute, Anders Svensson rolled an innocuous pass to Graeme Le Saux 30 yards from the United goal. The former England international produced a perfectly weighted pass forward to Rory Delap, whose shot from 12 yards was bravely blocked by United goalkeeper Tim Howard at point-blank range.
Saha's first real contribution had come seconds earlier when he found van Nistelrooy on the right, with the Dutchman's pace taking him past Fitz Hall before producing a low cross-cum-shot which spun along the Southampton line.
Saints skipper Jason Dodd capitalised on sloppy play by Paul Scholes on the right to send his 20-yard chip inches wide of the United far post.
The sub-plot involving Irish racing tycoon John Magnier and United manager Sir Alex Ferguson, which had dominated the papers all week, occasionally rose above the football with chants of "Stand up if you love Fergie" prompting an impressive response from the record Premiership crowd of 67,758.
Antti Niemi suffered his first worrying moment in the 16th minute when Scholes worked a neat one-two with Saha before firing in a 25-yard shot which was saved by the Southampton goalkeeper at full stretch.
But, two minutes later, the worry turned to despair.
Delap was adjudged to have pulled down Cristiano Ronaldo two yards outside the Southampton penalty area.
Saha stepped up to curl his left-foot shot goalwards with Phillips' header diverting the ball beyond Niemi and into the net.
Thoughts of United slipping into easy overdrive were soon dispelled as Anders Svensson and Brett Ormerod planted headers wide and Fabrice Fernandes fired a 25-yard shot into Howard's midriff.
But, as Southampton piled forward, they were caught cold by United in the 37th minute.
Saha started the move with a simple ball to Roy Keane. United's skipper turned it on to van Nistelrooy whose lay-off set up Saha.
The Frenchman's fierce 25-yard shot from the right side of the Saints box was only parried by Niemi and Scholes followed up to tuck away the rebound right-footed from eight yards out.
United's joy was short lived when Southampton hit back within a minute.
Phillip's whipped in a shot from 25 yards and, as Brett Omerod tried to beat United defender Mikael Silvestre, the ball took the slightest of deflections off the Saints striker to creep beyond Howard and into the net.
The second half continued in the same fashion as both sides fought to get a stranglehold on the game.
Saints equalised eight minutes into the second half with a goal which came out of nothing.
Phillips seemed to pose little threat when he picked up a loose ball 30 yards from goal, but his deceptive swerving shot bent away from the diving Howard and into the net.
United had it all to do again, but they had only seven minutes to wait before regaining the lead.
Ronaldo's free-kick from the right was handled by Fernandes on the line of the Saints box, although television pictures later found it to be inside.
United appeals for a penalty were waved away by referee Graham Barber and Ronaldo stepped up to take the second free-kick.
The Portuguese teenager fired the ball into the near post where Delap kicked it up into the air. Wes Brown pounced to knock it back into the centre where van Nistelrooy bundled his shot home off Dodd for his 99th goal for the Red Devils.
But the goal seemed to inspire Southampton and not United, whose defending became more and more slipshot.
A combination of Howard and Silvestre denied Omerod after he had capitalised on a mistake by Quinton Fortune.
At the other end, Saha's finely weighted throughball set up Scholes, who lured Niemi off his line before getting in a shot which fizzed inches wide of a post.
Saints brought on Marian Pahars and James Beattie and United's defending deteriorated even further.
In the 72nd minute, Anders Svensson brought a magnificent acrobatic save from Howard as he clawed away a blistering 30-yard drive from the Southampton midfield man.
Three minutes later, Paul Telfer found Beattie on the edge of the United box and his clever pass set up Phillips to force another good save from Howard.
As United fans' hearts missed beat after beat, the defending became more and more comical.
Silvestre lost the ball to Phillips on the right edge of the United box, but Brown saved the day with his intervening header.
Seconds later, an amazing sequence of events left Southampton's players holding their heads in disbelief at not having scored an equaliser.
Dodd's corner was completely missed by Howard. Pahars knocked the ball back from the far post and Danny Higginbotham's magnificent overhead kick from ten yards saw the ball crash off the bar before being hacked clear.
United were now reeling and when Beattie beat Silvestre in an crunching tackle on the right corner of the box, his low cross was turned away by Howard as Pahars moved in for the kill.
United did have one chance in the middle of this continuous Southampton pressure when Brown headed substitute Darren Fletcher's cross narrowly wide in the 84th minute, seconds after United's first corner of the game - a statistic which spoke volumes from an amazing match.
Man of the Match: Louis Saha – gave a superb all-round display on debut, proving he has the temperament to shine at Old Trafford.