Manager Steve Bruce is now hoping the first win of the new year will herald a rapid climb out of the relegation area in what has been a demoralising experience.
Without a win in their previous five games Birmingham battled out of an awkward situation when Pennant put them ahead after 25 minutes, with Mario Melchiot increasing this advantage with his first goal of the season after 33 minutes
Birmingham's problems have been identified by their crippling injury crisis but they had one bonus with the unexpected appearance of Matthew Upson who, on Saturday, had expected to be absent for at least a month with an ankle injury.
There have been significant failings primarily in attack but on this occasion Birmingham took full advantage of a Wigan side that is suddenly struggling to maintain their early season form.
They have suddenly started to flag. There was little improvement following a 3-0 home defeat at the hands of Blackburn and they were definitely off the pace against Birmingham.
The game itself took some time to come alive. Birmingham conspired to mount most of the attacks but wasted several good situations particularly from free-kicks.
Pennant was the main culprit in this respect and he was subsequently relieved of the duty when Australian Stan Lazaridis, in his last season at St. Andrew's, produced a more accurate free-kick which Emile Heskey headed over the bar.
But Pennant had the last laugh a few minutes later as the former Arsenal player was on hand at the far post to guide home his header from Jiri Jarosik's left-wing cross.
The response from Wigan was spasmodic. Josip Skoko managed to get one shot on target but on this occasion Birmingham's defence was not really tested by opposition who could find the last few months of the season a testing operation.
They conceded a second goal in the 32nd minute when Pennant's corner was headed clear only to Muzzy Izzet. The ball was deflected by Stephane Henchoz into the path of Melchiot to force his shot home from close range only to fail to appear for the second half.
Birmingham, desperate to maintain their advantage, dropped back on to the defensive. But this is not the strongest part of Birmingham's play.
Unfortunately Jason Roberts and Henri Camara were not fully on song and there was little chance of a positive second half revival.
Their plight should have conclusively been sealed eleven minutes into the second half, but Heskey wasted a fine opportunity but embarrassingly scuffed his shot.