The former RB Leipzig boss dropped to his knees in relief as he heard the final whistle of the match in which Danny Ings scored the only goal of the game after just two minutes.
The 53-year-old has turned things around at St Mary's following a damaging 9-0 defeat at home to Leicester 13 months ago, after which his future at the club was left in serious doubt.
Hasenhuttl has now opened up on his relationship with Jurgen Klopp, which shows why he was left filled with joy as he side claimed all three points on Monday evening.
The Austrian said: "It says everything and says we had an unbelievable mentality today, even more than they have.
"We never give up and try to the end to turn things around. We showed it is possible to win against such teams and we did it in a fantastic way and finally we needed to have a perfect evening and it was one.
"The good thing is you don't expect to take points from this team so that is like bonus points. For sure, it all comes together with the belief to take this win really.
"Until 80 minutes or so you think you have done a good job so far, but there is still a long way to go with winning and then with my history with Jurgen, he is the only coach I have never taken points off.
"So I was joking with him one month or two months ago when we had the Premier League meeting and I said 'I want to have the chance to take a point off you!'
"It is just a perfect evening. Because of the effort they maybe deserved to take a point but that is not important today. You take it and that is it."
Klopp chose to blame the officials after the match as a potential penalty incident involving Sadio Mane and a possible handball by Jack Stephens were not awarded by referee Andre Marriner.
The German boss said: ”I hear now that Manchester United had more penalties in two years than I had in five and a half years. I've no idea if that's my fault, or how that can happen.
"But it's no excuse for the performance. We cannot change it, we have to respect the decisions. But we can change our performance. That's our focus now."