CALLUM McManaman’s third-minute goal was enough to book Wigan Athletic’s place in the play-offs with a game to spare and give beaten Birmingham the Blues.
The young forward took advantage of some great work from Jordi Gomez to find the bottom corner of Darren Randolph’s net for the only goal on a night of drama at St Andrew’s.
Latics had come into the game on the back of back-to-back losses against Burnley and Blackpool.
But they were always too good for Lee Clark’s side who haven’t won at home since October and now require snookers to escape the drop on the final day.
Birmingham did have their chances, but Scott Carson pulled off a couple of fine saves to deny Emyr Huws in the first half and Hayden Mullins right at the death.
Latics can now rest players at Blackburn this weekend, knowing they can finish no lower than sixth spot in the table, and strong favourites to clinch fifth.
McManaman’s goal from the first attack of the game visibly knocked the stuffing out of the home side, with the sense of desperation on the terraces becoming increasingly apparent as time ticked by.
Boosted by the perfect start, Latics continued to push forward with confidence, with James Perch and Martyn Waghorn combining well down the right, and Beausejour and McManaman proving an effective combination down the left.
Shaun Maloney was tripped on the edge of the penalty area, which allowed Gomez the opportunity to line-up a free-kick from 25 yards.
The wall did its job and blocked the effort, with James McArthur seeing another shot deflected behind for a corner.
Latics then thought they had doubled their advantage when a scramble in the home area involving Perch and Waghorn saw the ball end up in the Birmingham net.
Unfortunately for Latics the whistle had already gone, a rather generous decision in favour of the goalkeeper for the merest suspicion of contact.
With half an hour gone, Carson was yet to make a save, but that soon changed as Huws steadied himself and took aim from 25 yards.
The young Welshman, on loan from Manchester City, has already scored a couple of absolute belters this season.
And he nearly added another to the collection with a delightful curling effort that was bound for the top corner.
Thankfully for Latics, Carson scrambled back and tipped the ball away magnificently to the dismay of the home players.
Latics ended the half on the front foot, and a great run across the field by McManaman nearly led to an opening for Maloney.
Blues made a change at the interval, man mountain Nikola Zigic for Lee Novak, and the back three of Gary Caldwell, Emmerson Boyce and Rob Kiernan knew what was on the way.
Still, though, Latics remained in charge and were asking most of the probing questions.
Waghorn led a break forward but couldn’t quite find McManaman, with McArthur again setting himself but firing just wide.
Maloney then played in Waghorn, whose shot found the side-netting rather than the back of the net, and that was the ex-Leicester man’s final contribution before being replaced by Marc-Antoine Fortune.
Birmingham briefly threatened when Zigic’s header flew straight at Carson, whose opposite number had to hare off his line to prevent Fortune having a clear goalscoring chance.
Latics ought to have made more of another attempted break, but Fortune sold Gomez hopelessly short which invited another push from the home side.
Huws tried his luck again from distance but the ball fizzed harmlessly over the top, before Nicky Maynard took over from McManaman for the visitors.
On-loan Manchester United man Federico Macheda looked like he had wriggled free for Birmingham in the final quarter, but Kiernan was across quick as a flash to shut the door.
And Latics were indebted to their goalkeeper twice in the dying seconds to keep them ahead, Carson denying first Huws and then, brilliantly, Mullins before the referee’s whistle finally sounded to the delight of the 994 travelling contingent from Wigan.
Latics: Carson; Boyce, Caldwell, Kiernan; Perch, McArthur, Gomez, Beausejour; McManaman, Maloney, Waghorn.
Subs: Al Habsi, Crainey, Barnett, Espinoza, Collison, Maynard (for McManaman, 83), Fortune (for Waghorn, 61).
Birmingham: Randolph; Caddis, Spector, Adeyemi, Hancox; Burke, Huws, Mullins, Allan; Novak, Macheda.
Subs: Doyle, Martin, Ibe (for Allan, 61), Reilly, Zigic (for Novak, 46), Shinnie (for Adeyemi, 83), Gray.
Star Man: Gary Caldwell