Wigan wiped the floor with beleaguered Birmingham in a horribly one-sided Sky Bet Championship encounter at the DW Stadium.
Callum McManaman was again the pick of the Latics players with two first-half goals as the home side led 3-0 at the break.
Andrew Taylor and substitute Martyn Waghorn grabbed the others for Wigan, who could have won even more comprehensively than 4-0 such was their total superiority.
Birmingham's best chance came with six minutes remaining, but Scott Carson pulled off stunning saves in quick succession to deny Paul Caddis and then Clayton Donaldson.
All of the pre-match talk had centred on James McArthur's proposed move to Leicester, which fell through on Friday.
And the Scotland midfielder was a driving force for his side after being given the nod by Uwe Rosler.
Wigan were ahead inside nine minutes when McManaman beat three men before drilling under goalkeeper Darren Randolph.
Oriol Riera and McArthur came close to making it two before Wigan did double their advantage six minutes before half-time.
McArthur played Taylor down the left, and the full-back launched an unstoppable drive that was past Randolph before he could move.
And it was game over as a contest when McManaman found the top corner from 15 yards to notch his fourth goal of the season.
The visitors made a decent start to the second half, with Caddis' shot being superbly blocked by Rob Kiernan on the edge of the area.
Caddis' corner found the head of Donaldson, who could only direct his effort straight at Carson.
Wigan hearts were in mouths shortly after when James Perch almost put too much on a back-header and was relieved to see Carson make the save on the line.
But after that normal service was resumed and Waghorn nearly scored with his first touch after coming off the bench, forcing a good save from Randolph.
More clever footwork from McManaman saw him wriggle free, but this time his shot was easily saved.
That was the young forward's final involvement before before making way for Shaun Maloney.
And the Scotland star made an instant impact, laying number four on a plate for Waghorn, who could not miss from four yards.
Maloney was at it again shortly after but he could not engineer a goal for McArthur, who fired into the side-netting from close range.
Emmerson Boyce saw a late header off Emyr Huws' corner tipped over by Randolph as Wigan went all out for a fifth.
That did not come, but they denied Birmingham even a consolation at the other end when Carson showed superb reflexes to deny Caddis and then Donaldson.