Mauricio Pochettino was denied his first win as Saints manager by a 90th minute equaliser from Shaun Maloney at Wigan.
Saints battered their relegation rivals after falling behind to a Gary Caldwell header from a corner in the first half.
But once again marking from set pieces let Saints down as Maloney popped up with the late leveller.
The game had been a midfield battle between two of the league's passing sides until Wigan created the first chance 13 minutes in.
Jean Beausejour swung over a great cross from the left and Franco Di Santo did brilliantly to get his toe to it and stab the ball towards the far post but Artur Boruc was equal to it.
With the DW Stadium waiting for an offside flag that never came, Ramirez slashed the ball well over the bar, and replays showed he was clearly onside.
The next opening produced a goal, with Beausejour again the architect. The Chilean's corner picked out the head of Caldwell, who, having engineered space, placed his header perfectly into the bottom corner.
Southampton almost levelled straight away in bizarre fashion when James McCarthy took too long over a clearance and smashed it against Schneiderlin.
The ball spun towards the top corner off the Southampton midfielder but Ali Al Habsi managed to claw it away just in time.
The scoreline was harsh on Saints and they dominated the final stages of the first half but were unable to find an equaliser. They came close twice, first Jos Hooiveld heading just wide before Jay Rodriguez's header was cleared by Caldwell at the far post.
Southampton boss Mauricio Pochettino made a change at the break, Steven Davis replacing Ramirez, who had picked up an injury at the end of the first half in a clash with Roger Espinoza.
The visitors continued to do most of the pressing and with a little over half an hour to go Wigan boss Roberto Martinez opted for a defensive reshuffle.
Jordi Gomez replaced Ronnie Stam, meaning Beausejour dropped back into defence, Maynor Figueroa moved into the centre and Scharner to right-back.
They continued to live dangerously, though, and Saints surely would have scored had Schneiderlin managed to connect properly with a cross from Lambert, who was proving a real handful for Wigan.
In the 60th minute, Adam Lallana entered the fray for Saints as he continued to work his way back from a knee injury, and four minutes later they had their equaliser.
Jack Cork crossed and Rodriguez outjumped the Wigan defence to head on for Lambert, who bravely beat Al Habsi to the ball at the back post.
Southampton sensed a vital win was there for the taking and they were inches away from going ahead in the 71st minute as Lallana pounced on a half-blocked effort and smacked his shot against the near post.
Wigan finally quelled the siege on Al Habsi's goal but Southampton were not to be denied and, from a Latics corner, Rodriguez burst away down the left, beat a lunging challenge from substitute Callum McManaman and crossed for Schneiderlin to smash home.
Wigan looked down and out but they refused to be beaten and with the match entering the 90th minute Scharner got his head to a corner and Maloney scuffed the ball over the line.