Newcastle had a goal ruled out from Joelinton for handbal in the first half. The Brazilian then missed a sitter early in the second half as the game remained goalless.
But it would prove to be third time lucky for Joelinton as he turned the ball in from close range following some great work down the right from Alexander Isak to set up the goal.
A minute later Southampton thought they’d equalised as former Magpies striker Adam Armstrong bundled the ball into the net only for it to be ruled out for handball following a VAR check.
Southampton were reduced to 10 men late on as Duje Caleta-Car was shown a second yellow card.
Here are the Newcastle player ratings from the match...
1. Nick Pope - 8
Had to be quick off his line to clear a Southampton through ball and was almost caught out by an Alcaraz shot from distance in the first half. Did well to deny Adams one-on-one in the second half and once again shortly after. Another crucial performance in goal.
2. Kieran Trippier - 6
Put a number of testing crosses into the box but no team-mate could get on the end of them. Passing was sloppy at times. Booked.
3. Fabian Schar - 7
Recovered from an early injury scare to keep Southampton at bay. Photo: Julian Finney
4. Sven Botman - 7
Should have done better with a back post effort but remained solid defensively.