Ayoze Perez had scored four in his last seven homes games as well as the winner at Leicester last weekend and he continued his fine run of form with a superbly taken hat-trick.
His first was a perfectly placed clipped shot, kissing the inside of the far post after Isaac Hayden had won the ball back in midfield.
He followed that up two minutes later as his determination to meet Salomon Rondon's low cross ahead of Ryan Bertrand bought him and his team a second goal.
After Newcastle had toiled in the second half, he completed his hat-trick with just four minutes left, poaching a close range header after Matt Ritchie had bravely dived in to win a rushed Southampton clearance.
Perez has now got 10 Premier League goals this season, the first Newcastle player to do so since Georginio Wijnaldum in 2015-16.
And it was ironic that Wijnaldum scored one of the goals (for Liverpool) against Cardiff on Sunday that made us safe from relegation.
Perez is the first Newcastle player to get a hat-trick since Dwight Gayle in December 2016
Newcastle boss Rafa Benitez: "The main thing was to win. I'm really proud of this group of players for working so hard.
"Ayoze has to be consistent but he is capable of doing this kind of thing [scoring hat-tricks] and has the quality."
Newcastle's hat-trick hero Ayoze Perez: "It's an unbelievable feeling to get three goals and get three important points. I need to thank my team-mates for the way we are playing and I am very proud of myself for the hat-trick.
"It's been a couple of months that are very important for us. We've done very well, We've got great results and now that we're safe we're going to start looking forward and up and finish even better."
This was Newcastle's sixth home Premier League win of 2019 - only Man City (8) and Arsenal (7) have won more.
Perez's hat-trick was Newcastle's first in the Premier League since October 2015, when Georginio Wijnaldum scored four times against Norwich City.