Henri Camara was not far behind. The on-loan striker from Celtic required only seven minutes to score his first goal for the Saints and it was another piece of outstanding finishing after being drafted into the side at the start of the second half.
But Birmingham sealed the points on the strength of their first-half performance although the Saints displayed courage and determination in their unsuccessful bid to earn a point.
It was obvious that following four successive Premiership defeats and only one win in their previous six games, Birmingham were in dire need of an injection of new blood and there is little doubt that Pandiani, the Uruguayan international striker, was just what the doctor ordered.
He demonstrated that he possesses speed, shooting ability and heading skill which paved the way for this important win which takes Birmingham into a safe position away from the threat of relegation.
Southampton, on the other hand, really have a fight on their hands. They were outgunned by a smarter Birmingham side in which Jermaine Pennant also made an immediate impact.
In the absence of Emile Heskey, who dropped out at the last minute, Birmingham's new-look side was obviously keen to make an impact.
On-loan Pennant may have his problems off the field but these were temporarily put on one side as he dazzled with his all-action play and he was involved in all parts of the pitch as he made a story-book debut.
It was the brilliant youngster from Arsenal who set up Pandiani as early as the eighth minute with a low cross which the former Deportivo La Coruna striker rifledcjust wide.
But in the 12th minute Pandiani made no mistake. Julian Gray made the early running with a cross to the right to Pennant and his head high ball back into the middle was headed past Antti Niemi for his first goal in the Premiership.
Niemi distinguished himself in brilliant style to prevent Birmingham adding to their lead in the 29th minute when Jamie Clapham saw his 30-yard swerving shot spectacularly finger-tipped over the bar by the Southampton keeper.
Under the guidance of new boss Harry Redknapp, the rapidly improving Southampton side were likewise keen to make an impact in what was a crucial game for both clubs but they were generally out-manoeuvred by Birmingham.
Redknapp, the ace wheeler-dealer, included his loan signing Olivier Bernard from Newcastle with Camara starting on the subs bench.
But the Saints had to play second fiddle for long spells as they gallantly denied Birmingham.
Striker Peter Crouch received little support and could make little impact.
Jamie Redknapp blotted his copy-book in the 39th minute when he impeded Mario Melchiot and Robbie Blake, another recent acquisition, hammered home the penalty to consolidate Birmingham's lead.
Camara, meanwhile, electrified the Southampton fans with a brilliantly taken goal in the 52nd minute when he raced onto a Jelle Van Damme pass to fire a rocket-shot into the top corner of the net.
David Prutton went close to an equaliser as Birmingham suddenly lost their first-half composure but the ever-present danger of Pennant enabled Birmingham to take the points.
Birmingham made hard work of their task in the latter stages and Stephen Clemence shot straight at Niemi from six yards but they held on to take three crucial points.