Sunderland striker Stern John returned to haunt his former club by snatching a dramatic late equaliser at Birmingham.
John came on as a substitute to make an impact for Sunderland
The Black Cats had gone behind when Paul McShane diverted a Stephen Kelly header into his own net.
Sunderland were denied a penalty for an apparent push on David Connolly before Michael Chopra clinically finished.
But Garry O'Connor angled in a shot to put the Blues ahead again only for John to nod home after heading against the crossbar just minutes earlier.
Sunderland showed no early signs of complacency after their opening day win against Tottenham as they chased and harried Birmingham with feverish intensity.
The home side did not shy away from the physical challenge and responded in kind as the game was played at a frenetic pace.
But the effort was not matched by quality as both the teams who were automatically promoted from the Championship last season cancelled each other out.
The deadlock was finally broken after 28 minutes when Sebastian Larsson flighted a free-kick into the Sunderland box and Kelly angled a header across the visitors' goal.
Black Cats defender McShane tried to move out of the way but could not help getting a crucial glancing touch off his chest as he diverted the ball past keeper Craig Gordon's dive and into his own net.
Sunderland tried in vain to respond and could have had a penalty when Connolly appeared to have been shoved by Kelly as the striker chased a high through ball on goal.
Birmingham almost added insult to injury as they almost extended their lead just before the break.
Chopra had one real chance and took it to score
Johan Djourou made space for himself to get in a near post header only to mistime his effort and send it high and wide.
Sunderland searched for an opening after the break and, to their credit, the visitors kept plugging away.
They were rewarded when Ridgewell missed an attempted headed clearance and Chopra stole in to finish with aplomb.
In an all-action finish to the match, substitute O'Connor cut inside before powering the home side ahead again after 82 minutes.
Sunderland refused to lay down and Carlos Edwards produced a piercing run and crossed for John, whose six-yard header struck the woodwork.
Nyron Nosworthy had a chance to net a late equaliser only to nod a far post effort just wide.
John made no mistake when given a second chance. Blues keeper Colin Doyle did well to save a deflected Ross Wallace free-kick but Nosworthy got to the loose ball and headed across to John, who nodded in.
But, despite Doyle and his team-mates protesting that the keeper was impeded as he tried to get to the ball, the spoils were shared.
Birmingham manager Steve Bruce:
"Colin Doyle has produced a fantastic save and he was impeded from getting up.
"Everyone in the ground seems to have seen it apart from the referee who was 10 yards away.
"It's bitterly disappointing because we thought we had notched our first Premier League win and we know how precious they are."
Sunderland boss Roy Keane:
"The performance was not great. Maybe that was expected after the big high of the weekend in beating Tottenham.
"But once again the players scored so late in the game and deserve credit for having that desire and determination for getting a result which didn't really look possible.
"We need all the squad of players pulling together."
Birmingham: Doyle, Parnaby, Djourou, Ridgewell, Kelly, Larsson, Muamba, Nafti, McSheffrey (O'Connor 65), Forssell (Jerome 84), Kapo.
Subs Not Used: Maik Taylor, Jaidi, Vine.
Goals: McShane 28 og, O'Connor 82.
Sunderland: Gordon, Collins, Nosworthy, McShane, Halford (O'Donovan 70), Edwards, Etuhu, Whitehead (Miller 58), Wallace, Connolly (John 58), Chopra.
Subs Not Used: Ward, Anderson.
Goals: Chopra 75, John 90.
Ref: Keith Stroud (Hampshire).