The Swans were in the ascendancy in the first half when Vipotnik volleyed in from Josh Tymon’s cross, only for the Slovenian striker to be flagged for offside.
Replays showed Vipotnik was being played onside by Birmingham centre-back Christoph Klarer.
The home side went on to snatch a dramatic late victory as substitute Lyndon Dykes headed in four minutes into added time.
The Scotland international produced a trademark far-post header from Patrick Roberts’s cross as the hosts responded to back-to-back league defeats.
The defeat was Swansea’s first since they lost at the Riverside Stadium to Middlesbrough on the opening weekend of the season ending an unbeaten run of seven games in all competitions.
In a game of fine margins, Sheehan felt the Swans had been unfortunate to fall on the wrong side of the result.
“We’ve had a week of downs and ups and another down, but that’s the way it is. The players gave absolutely everything,” said Sheehan after the match.
“I think we caused them problems. In the first half, we had enough chances.
“I believe the decision when we scored was incorrect. From what I’m hearing, he [Vipotnik] is [onside].
“I’m not going to make it all about one decision, but I suppose in a game like this, when two teams are going after each other, I think you’ve got to get them right whatever the outcome is.
“You’re coming to Birmingham, who are in in a good place at home, not lost in a long time, but I think we came here, and we caused them some problems.
“Did we come away from what we were doing well in the first half? Potentially.
“There was not much in it, and again I cannot fault the application and the effort of the players.
“But they went a bit direct, brought on a bit more size and then with a spare man in the box they produced the one bit of quality that was the difference.”
[Lead image: Swansea City FC]
