Ward beat Guly Do Prado to George Thorne's looping header to nod past Kelvin Davis with six minutes remaining to cancel out Rickie Lambert's opener for Saints and secure a the beleaguered Fratton Park outfit a point.
With the impending threat of a possible points deduction hanging over Portsmouth's head as former chairman Vladimir Antonov is investigated by financial officials in Lithuania, the Pompey crowd needed a boost like that given to them by Ward against their bitter rivals.
And, having been dominated for long periods by their promotion-chasing guests, Portsmouth manager Michael Appleton will have been delighted by his team's resolve and determination not to give up.
Southampton had plenty of chances to put the game out of their hosts' reach after Lambert's 63rd minute strike, but Do Prado, Morgan Schneiderlin and Adam Lallana all wasted good opportunities, before Ward netted late on.
In front of a lively crowd, evidently relishing the relatively rare occurence of this fixture, neither side could really create any chances of major significance early on.
Lambert nodded Dean Hammond's centre harmlessly over after 14 minutes for the visitors, while at the other end Ward's attempt was comfortably saved by Davis eight minutes later.
Southampton had been struggling on the road of late, with defeats at Bristol City and Doncaster hampering their charge to promotion.
And they were more than matched by their close rivals for much of the first half, despite Saints starting the game with almost double the number of npower Championship points.
Stephen Henderson in the Pompey goal was not too bothered by Lambert's second attempt midway through the first period, and David Norris was denied by Davis as half-chances were as much as the baying crowd were allowed in the first 45 minutes.
With half-time approaching, full-back Greg Halford fired over the bar for the hosts and Norris sent a shot narrowly wide of the left-hand post two minutes before the break.
After the two teams went into the interval goalless, Southampton turned on the pressure in the opening minutes of the second period.
Lambert saw his effort from the edge of the penalty area saved by Henderson, while the Portsmouth keeper also had to be alert to prevent Schneiderlin's attempt sneaking in.
The waves of Saints attacks kept coming, however, and Lallana sent a shot from 16 yards over the crossbar as the league leaders cranked up the intensity.
And just after the hour their ascendancy finally told on the scoreboard.
Daniel Fox delivered the cross and Lambert stole in away from his marker to head beyond Henderson from close range.
It was all Southampton deserved for their intrepid play after half-time, and the visitors did not seem content to stop there.
Frazer Richardson saw his shot blocked by Joe Mattock, Hammond's 30-yard daisy-cutter was not powerful enough to cause Henderson any concern and Do Prado's miscued volley bobbled wide of the right-hand post as Pompey found it hard to create anything of note at the other end.
Henderson did well to get out to deny Do Prado when he was played in by Lallana, while Schneiderlin crashed over when well placed, and it seemed only a matter of time before the Saints grabbed their second.
However, out of nowhere, Portsmouth equalised with six minutes remaining.
Norris looped in a corner from the right, Thorne headed the ball back across goal and Ward showed the determination to beat Do Prado to the aerial ball and nod beyond Davis to extend Pompey's unbeaten run to four matches.