The pair fighting for Premier League survival are both left on 23 points, which is level with Burnley and four ahead of Cardiff City occupying the first relegation spot.
Zaha fizzed a low shot past former Eagles man Alex MCarthy to put Palace ahead on 41 minutes after Andros Townsend had set up the move.
Palace looked set to claim all three points in what would’ve been a crucial victory at St Mary’s, but Jan Bednarek cleared Mamadou Sakho’s close-range shot off the line.
Ward-Prowse, who has scored in each of the last three Premier League games, then cancelled out Zaha’s earlier tally in the 77th minute, when he hit first-time from Matt Targett’s ball back across the box.
Zaha would be sent off nearing full-time for a pair of yellow cards, the first coming following a clash with Ward-Prowse and the second for sarcastically clapping at referee Andre Marriner.
Southampton: McCarthy, Targett, Stephens, Vestergaard (Elyounoussi 75), Bednarek, Valery (Armstrong 62), Hojbjerg (Slattery 84), Romeu, Ward-Prowse, Redmond, Ings.
Unused subs: Gunn (GK), Ramsay, Long, Gallagher.
Bookings: Hojbjerg (37), Bednarek (59).
Crystal Palace: Guaita, van Aanholt, Sakho, Tomkins (Dann 90+1), Wan-Bissaka, McArthur, Kouyate (Schlupp 71), Milivojevic, Zaha, Townsend, Ayew.
Unused subs: Hennessey (GK), Kelly, Meyer, Wickham, Benteke.
Goals: Zaha (41).
Bookings: Milivojevic (35), Bissaka (47), Zaha (87, 87).