Ayoze Perez sealed a huge three points for Newcastle United against one of their relegation rivals to secure Premier League safety.
Perez opened the scoring on 28 minutes from a difficult angle.
Perez got his second of the game at the back post after 31 minutes.
Mario Lemina got one back for the Saints after 59 minutes.
Newcastle's number 17 got his hat-trick in the 87th minute.
The story of the game
The home side forced Angus Gunn into a smart save after nine minutes when Miguel Almiron fired one from a tight angle.
On 22 minutes Nathan Redmond got in behind the Magpies' defence before pulling the ball back for James Ward-Prowse who saw his shot blocked by Matt Ritchie.
Southampton were lucky to still have 11 men on the pitch when Ward-Prowse deliberately blocked off Miguel Almiron on the halfway line when himself and Salomon Rondon would have had a two-on-one against Gunn.
The Magpies got the opening goal through Perez as he picked up the ball near the edge of the box and cutely finished into the far corner off the post.
Isaac Hayden won the ball back in midfield with some sharp closing down which won Newcastle the ball back.
Perez doubled his and the Magpies' lead when Rondon burst down the left-hand side and put in a great cross on the floor to Perez who slid in at the back post.
Ki Sung-Yueng tried his luck from the edge of the box five 10 minutes into the second half but he saw his shot cannon back off the post.
Lemina curled a shot into the bottom corner just before the hour mark as the Magpies did not track their runners as the half time substitute halved the deficit.
The Saints had a chance to level things up when a corner found Redmon who dinked it back in for Maya Yoshida however, the centre back could only fire his close-range effort over the bar.
Hayden caught the ball on the volley 20-yards out which took a deflection but Gunn was equal to it as he pulled off a magnificent save.
The Saints dominated the second half but the Magpies got their third of the game through Perez.
The Spaniard directed a header goalwards after Ritchie's diving header from near the edge of the box went straight to Perez.
Perez the man for Newcastle once again
Just like last week Perez turned up in a big match for Newcastle once again grabbing the winning goal for the Magpies.
The Spaniard got his first hat-trick for the club against the Saints and it was what he deserved after a fantastic performance which showed why Rafa Benitez always puts him in the starting 11.
End of the season will come at a good time for the Magpies
Newcastle are walking wounded at the back with Florian Lejeune already sidelined and with Fabian Schar going off injured it leaves Benitez with just two fit centre backs.
Almiron also went off with a suspected hamstring injury as well as Hayden limping off the pitch in the second half leaves the Magpies with a minor injury crisis.
Man of the match
There is only one candidate for this and that is Perez who put in a marvellous display to all but secure Newcastle's place in the Premier League next season.
The Spaniard had three chances and took all of them as he put Southampton to the sword.