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...
9. Miguel Almiron - 6
Made some good runs down the wing to create opportunities for his team-mates but looked tired before being substituted. | AFP via Getty Images
10. Joelinton - 7
Very unlucky to have a goal ruled out. Kept Southampton busy down his side but missed a sitter early in the second half. Finally gave Newcastle the lead with a simple tap-in. | Getty Images
11. Callum Wilson - 5
Will have been frustrated not to have buried his chance in the build-up to Newcastle’s disallowed goal. Another quiet game without a goal. | Getty Images
12. Allan Saint-Maximin - 6
On for Willock 67: A great run saw Southampton go down to 10 men late on. Booked. Photo: OLI SCARFF