Just seconds after manager Rafa Benitez put on Fernando Torres as an extra attacking threat, Ba met a highbouncingball in the area and turned in the air to slot the ball past the diving Pantilimon.
Matt Gidley's obstruction on Richie Barnett denied Dean McGilvray a try for Saints but they drew level when Smith's bouncinghighball caught Warrington's defence unaware and Wilkin touched down.