David Connolly scored on his debut and Jimmy Bullard hit the winner to give Wigan victory at West Brom.
West Brom had taken the lead as Jonathan Greening volleyed into the top corner on 26 minutes.
But Connolly restored parity 14 minutes later with a superb rising drive after racing on to Damien Francis' pass.
West Brom's Thomas Gaardsoe headed wide just before half-time, but Bullard scored with a low shot in stoppage time to seal Wigan's comeback.
The reception for Wigan's former West Brom striker Jason Roberts was mixed, while the Wigan supporters roundly booed Baggies' former Wigan man Nathan Ellington.
Connolly was another under pressure in his first Premiership match following his move from Leicester.
He looked lively all game - quickly adjusting to life in the Premiership - but for much of the first half, his team-mates were off the pace.
The hosts, however, were in tenacious mood, picking up three bookings in the first 20 minutes.
And it was their dogged determination which paid off when Greening put them ahead.
After crashing a shot at a defensive wall, he quickly latched on to the rebound to smash home a shot to end his personal goal drought - and notch his first for Albion.
Less than 15 minutes later, Connolly also opened his account for a new team.
Sprinting on to Francis' pass, Connolly rifled a shot into the top left corner to score his first Premiership goal.
The equaliser was just about deserved as Wigan battled to get a foothold in the game.
But they were lucky not to go into the break 2-1 down when they left Gaardsoe unmarked in the area, but he nodded wide when he really should have scored.
Early in the second half, Ellington saw his fizzing effort tipped over as West Brom looked to up the pace.
But with both sides desperate not to lose, risks - and opportunities - were rare.
It took until halfway through the second period for another chance to come, but Richard Chaplow's 25-yard shot flashed wide.
But despite the introduction of Kevin Campbell and Robert Earnshaw, it was Wigan who started to look the more likely to snatch a winner.
Especially when Earnshaw embarrassed himself by swinging and missing in the penalty area.
However, it was a late, late strike which shocked West Brom as Bullard slotted a precise shot into the bottom corner after Roberts had picked him out with a smart pull-back.
West Brom boss Bryan Robson:
"This was not good enough from my players and we will be going back to basics.
"They have kidded me because in the first couple of games of the season we started where we left off last season.
"But the last three matches are not acceptable as far as our defending is concerned. The frailty with which we are giving goals away is really poor."
Wigan boss Paul Jewell:
"It's a big thing to win away from home. Whatever win you pick up away, it's always a bonus.
"We felt at half-time we could win the game, particularly after finishing the first half quite strongly and scoring our first from open play this season.
"From our point of view both goals were good ones because they were well worked, giving us a big three points."
West Brom: Kirkland, Albrechtsen, Gaardsoe, Clement, Robinson, Watson, Greening, Carter (Chaplow 57), Wallwork (Campbell 71), Horsfield, Ellington (Earnshaw 71).
Subs Not Used: Curtis Davies, Kuszczak.
Booked: Wallwork, Horsfield, Gaardsoe.
Goals: Greening 26.
Wigan: Pollitt, Chimbonda, Henchoz, De Zeeuw, Baines, Bullard, Kavanagh (Taylor 79), Francis (Skoko 89), McCulloch, Roberts, Connolly.
Subs Not Used: McMillan, Jackson, Walsh.
Goals: Connolly 40, Bullard 90.
Ref: M Clattenburg (Co Durham).