The Saints skipper struck to make it 2-2 six minutes into stoppage time after the Magpies found themselves on the wrong end of a VAR decision for the third successive Premier League game.
It was no more than the visitors deserved after out-playing and out-thinking their hosts for much of a contest they probably should have won at a canter, but found themselves chasing after Callum Wilson and Allan Saint-Maximin had struck either side of Mohamed Elyounoussi’s equaliser.
Newcastle head coach Bruce, who endured chants of “We want Brucie out” during a dreadful first half, must have thought his luck had changed when Saint-Maximin scored as the clocked ticked into added time, but Ward-Prowse ensured his side are still awaiting their first victory of the campaign.
Southampton were on the front foot from the off with Oriel Romeu probing from deep to allow the men in front of him to try to stretch the home defence, although Magpies old boy Adam Armstrong was unable to make the most of an 11th-minute half-chance when he fired tamely wide on the turn.
They should have been ahead with 23 minutes on the clock after the ball broke for marauding full-back Tino Livramento inside the penalty area and he crossed for Moussa Djenepo who somehow managed to steer it over the crossbar from three yards.
Only a last-ditch block by Federico Fernandez denied Djenepo two minutes later with the Newcastle rearguard in disarray, as the home crowd turned on their manager.
Jacob Murphy whipped a 32nd-minute free-kick just over the crossbar after Saint-Maximin had been felled by Kyle Walker-Peters to quell some of the discontent, although Freddie Woodman had to save from Elyounoussi eight minutes before the break.
Wilson, who had endured a frustrating first half, drilled a 42nd-minute effort over after Saint-Maximin had made the most of Matt Richie’s clearance and then produced a fine save from Alex McCarthy after meeting Sean Longstaff’s near-post corner, but those openings proved rarities for his side.
Saint-Maximin blasted into the side-netting within seconds of the restart as Bruce’s men returned with a point to prove, but Fernandez had to block Armstrong’s 50th-minute effort and could only look on as Djenepo curled the loose ball just past the far post.
However, it was Newcastle who took the lead five minutes later when Jacob Murphy turned Fabian Schar’s cross back across goal and Wilson dived to head past McCarthy.
The goal did little to change the pattern of the game as the visitors remained patient and methodical in their approach and they got their reward with 16 minutes remaining when Elyounoussi slid in at the far post to stab substitute Nathan Redmond’s cross past Woodman.
However, the drama came at the death when substitute Ryan Fraser’s shot was cleared off the line and Saint-Maximin followed up to smash home what looked like the winner.
That was until referee Paul Tierney was asked to have another look at Jamaal Lascelles’ challenge on Armstrong and handed Ward-Prowse his chance to claim the late point.