Jordan Pickford's mistake cost Sunderland two points as he let a Jay Rodriguez shot through his fingers to allow Southampton to come from behind to draw 1-1 at St Mary's on Saturday.
Jermain Defoe had given Sunderland the lead from the penalty spot with 10 minutes left after being fouled by Jose Fonte, but the visitors were in front for just five minutes before substitute Rodriguez - this week linked with a loan move away - struck his first Premier League goal since March 2014.
Pickford had made several saves to keep his side in the game and there appeared to be little danger when Rodriguez let fly, only for the shot to somehow slip through the young goalkeeper's hands.
Matt Targett almost hit a dramatic winner for Southampton, but his free-kick went just wide of the post, with both teams still waiting for their first league win of the new season as a result of the draw.
Southampton started the better side and Dusan Tadic fired over the angle after 10 minutes.
The hosts' pressure continued as Charlie Austin, handed a start up front in place of Shane Long, ran on to a Tadic pass and forced a good save from Jordan Pickford.
Austin was looking lively and the striker let fly again after 17 minutes, only to be denied by Pickford, who had come into the Sunderland side for the injured Vito Mannone.
Sunderland had their first clear sight of goal after 25 minutes and Lamine Kone should have scored, but his back-post header from a Patrick van Aanholt cross flew narrowly wide.
In the same incident, Sunderland could have had a penalty when Fabio Borini appeared to be pushed over in the box by Fonte, but referee Lee Mason was unmoved.
Jack Rodwell missed the target with a glancing header from Adnan Januzaj's centre, then Cedric Soares tested Pickford with a long-range drive after 37 minutes.
The second half was also a close affair, with Papy Djilobodji's acrobatic effort drifting wide, although he was offside anyway.
Fraser Forster comfortably saved a low Fabio Borini free-kick after 62 minutes as the visitors briefly threatened, but the chances of an opening goal for either side appeared to be remote.
Pickford continued to catch the eye by keeping out efforts from Nathan Redmond and substitute Long, the latter save particularly impressive, and the goalkeeper's heroics proved vital as Sunderland edged ahead.
There appeared little danger when a ball came into the Southampton box, but Fonte hauled Defoe down and the striker smashed home from 12 yards.
It should have been a winner for Sunderland, but Southampton got level when Rodriguez's drive was fumbled into the net by Pickford.
Targett's set-piece almost completed a remarkable turnaround for Southampton, before Oriol Romeu's goalbound effort was blocked, but Sunderland held on for a point.