Ryan Taylor’s brace (15 and 55) – doubling his top-flight tally – and the foolishness of captain Damien Johnson, sent off after 37 minutes, sealed Birmingham’s downfall.
With his side trailing 1-0 late in the first half after Taylor’s confident left-foot finish, Johnson launched into an ugly two-footed lunge on Kevin Kilbane and was rightly sent off.
Wigan’s second goal was a scrappy effort, with Taylor eventually forcing the ball over the line after a major scramble.
Alex McLeish will be relieved Bolton were also beaten, maintaining Blues’ four-point cushion above the drop zone.
For Wigan, that gap is now eight points, enough to all but guarantee they will start next season in the top flight.