The Saints have been in excellent form in recent weeks, and despite the absence of star man Danny Ings, a goal in either half from Che Adams and Stuart Armstrong secured another three points.
Ralph Hasenhuttl’s side were quick out of the blocks in this one as Adams edged them in front on seven minutes.
Miguel Almiron gave away possession on the edge of the box, and Theo Walcott’s neat cut back was fired home by Adams.
The impressive Walcott looked to be on a mission from there as Moussa Djenpo’s flick sent him through, but his effort curled just wide.
The home side continued to push and push Newcastle after the break, as Oriol Romeu’s powerful effort clipped the bar and Jan Bedranek forced a fine stop from Karl Darlow.
With the Magpies unable to muster up a response, Southampton grabbed a deserved second with nine minutes to go.
Again, Newcastle played themselves in trouble as Sean Longstaff gave away the ball in a key area and Scottish international Armstrong tiptoed past Jamal Lasacelles and tucked home.
Newcastle did almost steal a late consolation, but the redundant Alex McCarthy produced a brilliant save from Joelinton.
Full Time at the St. Mary’s Stadium it’s Southampton 2 Newcastle 0