Wigan took its biggest step yet towards Premier League survival and left Birmingham sweating over relegation as the visitors self-destructed in a 2-0 result at the JJB Stadium.
Ryan Taylor's brace - doubling his top-flight tally - and the foolishness of captain Damien Johnson sealed Birmingham's downfall.
With his side trailing 1-0 late in the first half, Johnson launched into an ugly two-footed lunge on Kevin Kilbane and was rightly sent off.
Birmingham boss Alex McLeish will be relieved Bolton was also beaten, maintaining his side's four-point cushion above the bottom three.
For Wigan, that gap is now eight points, enough to all but guarantee it will start next season in the top flight.
Separated by just a point immediately above the drop zone before start of play, today's match was arguably the most important of the campaign for these two sides.
There was also the added spice of Latics boss Steve Bruce's reunion with the club he managed for almost six years before November's acrimonious departure.
Martin Taylor returned to the Birmingham line-up for the first time since his horror tackle on Eduardo.
The centre-back had not featured since breaking the Arsenal striker's leg on February 23.
After an opening 10 minutes bereft of quality, a Latics free-kick eventually led to the first chance of the game.
The Blues failed to clear Ryan Taylor's centre and Mario Melchiot's cutback was blazed over from eight yards by Marcus Bent.
Wigan then began to exert some pressure, which told as quickly as the 15th minute.
Antonio Valencia showed great vision to pick out Ryan Taylor at the far post following a superb jinking run down the right.
On his weaker left foot, Taylor confidently finished first time into the bottom corner - his first goal since Boxing Day.
Birmingham's defending was bordering on the shambolic, Kilbane allowed to burst from midfield and Heskey given plenty of time to strike a loose ball left-footed at Maik Taylor.
Birmingham's first shot on target was a 25th-minute Gary McSheffrey effort straight at Chris Kirkland from 20 yards.
The visitors were second best in every area, Bent reacting quickest to another Melchiot cutback before seeing his finish blocked.
With less than 10 minutes of the half remaining, the game was interrupted by a major flashpoint thanks to Johnson's moment of madness.
Johnson, who threw his armband off in disgust as he left the field, got plenty of the ball but the recklessness of his tackle on Kilbane warranted his ejection.
Kilbane nearly exacted revenge immediately from the restart, the Irishman sending a loose ball crashing against the inside of the post from 20 yards.
With little over a minute of the half remaining, Melchiot and Bent combined again, the former Blues full-back's cross steered a foot wide by the forward.
There was still time for the visitors to almost snatch an equaliser, the in-form Mauro Zarate narrowly off target from the edge of the area.
Heskey could have doubled Wigan's advantage straight from the restart, the England striker shrugging off his marker and firing a left-foot half-volley wide.
It was a further 10 minutes before the second goal arrived via one of the untidiest goals of the season.
Valencia's cross was nodded off target by Bent but Wigan somehow stopped the ball going behind and it found its way back to the goalmouth.
A major scramble ensued, which Ryan Taylor won to force the ball over the line.
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