Following Jonathan Walters's opener, the centre-back scored a late equaliser to earn the Black Cats a 1-1 draw at the Stadium of Light on Monday night, after Craig Gardner had earlier been shown a straight red card for a bad challenge on Charlie Adam.
The point lifts Sunderland three points clear of the relegation zone having played a game more than 18th-placed Wigan Athletic, who face Swansea City in their game in hand on Tuesday night.
"I hope it's very valuable," O'Shea told Sky Sports News. "We have to make sure we focus on Southampton now.
"It's a massive game again at home. We've got knocks and suspensions, and we'll dust ourselves down and go again."
Sunderland host Southampton on Sunday before travelling to Tottenham Hotspur the following weekend in their remaining two fixtures.