Jay Rodriguez was the man to open and wrap up the scoring, and he could easily have had a hat-trick by the interval as the Saints swarmed all over the disjointed Magpies.
Rickie Lambert added a second early in the second period and Adam Lallana a spectacular third to ensure that Mauricio Pochettino's hosts clambered above their weekend opponents and into eighth spot.
Alan Pardew was back in attendance after serving a stadium ban, but it was an unhappy return for the Newcastle manager to his old stamping ground as his current employers never got going.
Rob Elliot, in for the injured Tim Krul, was the only man to emerge with any credit for Newcastle as he single-handedly kept the scoreline down with some inspired reflex saves.
There was, however, little he could do in first-half stoppage time as Lambert sprung the offside trap and squared for Rodriguez to bobble home from close range.
Lambert then got in on the act himself four minutes after the re-start, with Lallana looping the ball over the back of a statuesque Newcastle back line for the England striker to crash into the roof of the net.
Lallana's effort on 70 minutes proved to be the pick of the bunch, with the talismanic midfielder allowed to carry the ball to the edge of the box before unleashing an unstoppable drive into the top corner.
Newcastle were all over the place at the back and it came as no surprise to see them breached again before the full-time whistle, with Rodriguez freed by another simple ball over the top to drill under Elliot.
The home fans thought they had a goal to celebrate after just eight minutes, only for it to become clear that Rodriguez had hit the side-netting.
He powered a header just wide soon after, before Elliot prevented him directing home a Lambert cross.
The Newcastle keeper was getting no respite from his defence and produced a fine reaction save when Lambert went through one-on-one.
The Magpies began to settle but were creating little and looking shaky at the back.
Elliot had to pull off another incredible save to deny a close-range Rodriguez header before he finally found a way through.
Lambert beat the offside trap to latch onto a Steven Davis ball over the top, bearing down on goal and squaring to the unmarked Rodriguez, whose effort may have been scuffed but finally beat Elliot.
Pardew will have no doubt given his players a dressing down at half-time and took off the ineffective Mapou Yanga-Mbiwa and Hatem Ben Arfa.
The introduction of Davide Santon and Luuk de Jong did little to stem the tide, though, with Lallana clipping over a fine ball to Lambert, who again beat the offside trap and stabbed past Elliot at his near post to double the hosts' advantage.
Moussa Sissoko flashed a strike across the face of goal as he tried to give the away fans something to shout about, before Papiss Cisse somehow avoided retribution for a late challenge on Calum Chambers.
Luke Shaw also hit the deck after a Sissoko challenge but it was not until the 76th minute that Andre Marriner - in his first outing since a red card fiasco at Stamford Bridge - finally went to his pocket, giving Massadio Haidara a booking for a late challenge on James Ward-Prowse.
By that point, the match had been put to bed by a moment of magic from Lallana. Collecting the ball deep in the visitors' half, he pushed on and unleashed a wonderful 25-yard strike.
Saints continued to press and Elliot produced another wonderful save to tip over a Ward-Prowse follow-up strike after Rodriguez had hit the woodwork.
A brave Shaw block denied Yoan Gouffran a late consolation at the end of a match that got worse for the visitors when Rodriguez cut back and fired through Elliot's legs with a minute remaining.