Hasenhuttl was brought in after Mark Hughes was sacked on Monday and, mindful that the Titanic had sailed from Southampton, spoke of not “hitting any icebergs” at his first press conference.
But Southampton were sunk by the sort of mistake which has left them in the choppy waters of the relegation zone and cost Hughes his job.
There seemed no danger in the 74th minute when Jannik Vestergaard was in control and seemingly shepherding the ball back to his goalkeeper Alex McCarthy.
Referee Jon Moss was considering bringing the play back for a foul on Cardiff’s Victor Camarasa, but the big Danish centre-back made a hash of his possession.
The split-second was all that Paterson needed and the striker, who was signed as a right-back and who still fills that position for Scotland, nipped in to beat McCarthy for his fourth goal of the season.
So it was the same old story for a Southampton side who have won only once in the Premier League this season and drop to 19th place, five points adrift of upwardly mobile Cardiff.
The Saints saw claims for a penalty refused after Stuart Armstrong took a tumble on the hour, but Hasenhuttl – the first Austrian to manage in the Premier League – knows he has his work cut out to turn around their fortunes.
Apart from a spell at the start of the second half, Southampton were second-best against opponents who have now won four of their last five home games and appear to be delighting in proving wrong those critics who wrote them off in August.
Hasenhuttl sprang a major surprise by making no fewer than six changes, and the Saints resembled a team that had just been introduced to each other during a disjointed first period.
Charlie Austin flicked wide two early half-chances, but Cardiff should have been ahead in the 10th minute when Josh Murphy began his torment of rookie right-back Yan Valery.
Murphy and Camarasa combined and Nathaniel Mendez-Laing hooked the ball back at the far post for Harry Arter to send a weak volley straight at McCarthy.
There was another escape for Saints when Jan Bednarek was caught dozing by Paterson and Valery did just enough to prevent Murphy getting his shot away.
Southampton offered little threat until Paterson’s miscued clearance from a corner looped onto the Cardiff crossbar and Mario Lemina sent the rebound over on the volley.
But Cardiff finished the half on top and Mendez-Laing’s firm attempt was acrobatically tipped over by McCarthy.
Southampton called for a penalty on the hour when Camarasa left a leg dangling and Stuart Armstrong went over it, but referee Moss was not interested.
It proved a decisive moment as Vestergaard’s colossal mistake was punished and Morrison should have added to Saints’ misery when he planted a free header wide from eight yards.
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