Birmingham's new-found confidence was highlighted by the fact that they scored more than two goals in a match for the first time this season.
They took full advantage of an injury-ravaged Sheffield Wednesday side which suffered its second defeat in five days. They also had Jimmy Smith sent off for a bad tackle.
As a result Birmingham, watched by their lowest home attendance of the season, increased their unbeaten record to six games as they consolidated their top of the table position.
Scotland international O'Connor, boosted by another vote of confidence from Alex McLeish, had another outstanding game for Birmingham with his two first-half goals paving the way for the latest win.
Goals at St Andrew's have been in short supply this season but not on this occasion when the fans were treated to three in a four-minute spell in the first half.
O'Connor, leaner and fitter than at any time in his career, opened the scoring in the 11th minute with a well-directed header from Seb Larsson's free-kick.
Wednesday immediately hit back with Etienne Esajas ramming home a 14th minute free-kick for his fifth goal of the season.
This was only the second opposition goal scored at St Andrew's this season and the response from Birmingham was to regain the lead a minute later.
The in-form O'Connor was again on the mark. His first shot was blocked but he immediately hit home the rebound with another accurate finish to make him the man of the moment at Birmingham.
Only a desperate save by Lee Grant prevented Kevin Phillips notching a third just after O'Connor's second strike.
Phillips again went close to increasing Birmingham's lead only to shoot wide when challenged by Tommy Spurr who was making his 100th appearance for Wednesday.
The former Sunderland and West Bromwich Albion striker, however, could not be denied and, in the 38th minute, he latched onto a long pass form Frank Queudrue to shoot low to the right of Grant.
Following their bright start, when Leon Clarke was a danger-man, the Owls struggled to put their game together as Birmingham attacked in depth in a bid to consolidate their lead but they had no answer to the Midland club's fire-power.
Clarke went close to scoring in the second half. He beat Maik Taylor only to watch Liam Ridgewell calmly run the ball out of danger.
Wednesday's tale of woe was complete when Smith, booked only six minutes previously, was given a straight red card by the referee for a bad tackle on Stuart Parnaby.