Calderwood's hat-trick proved crucial for the Warriors
Bradford: (22) 30
Tries: Solomona 3, Tupou, I Harris
Goals: I Harris 5
Wigan: (6) 31
A late Pat Richards drop-goal sealed a sensational victory for Wigan in their Super League play-off tie at Bradford.
Tries: Leuluai, Calderwood 3, Hansen
Goals: Richards 5
The Warriors looked down and out when they trailed 30-6 early in the second half after David Solomona had bagged a first-half hat-trick for the Bulls.
But Mark Calderwood emulated Solomona after the break as Brian Noble's side somehow got back on level terms.
Then, with just four minutes to go, an ice-cool Richards sealed a momentous victory with a superb drop goal.
Solomona gave the fired-up Bulls the perfect start with an early try, going over for the third consecutive game after taking Andy Lynch's pass.
Wigan tried to get back into the game but Bradford started to pile pressure on their opponents with Solomona proving influential down the left.
The New Zealander's kick was fumbled by Mark Calderwood in the air and Tame Tupou pounced to score.
Wigan hit back when Trent Barrett's long pass was grabbed by David Vaealiki who broke downfield and passed the ball inside to the supporting Thomas Leuluai.
But Solomona ensured the Bulls finished the half on a high with two tries in the space of four minutes.
First he forced his way over the line and although Wigan's Micky Higham looked to have got his body under the ball, video referee Phil Bentham gave him the benefit of the doubt.
Then he took Iestyn Harris's pass and stretched out to put the ball on the line for his first hat-trick for the Odsal side.
Wigan had to score first after the break and Calderwood went close but Bradford broke straight down the other end and Glenn Morrison's support play allowed Iestyn Harris to go over and then add the extras.
A penalty against Sean O'Loughlin allowed Harris stretch the lead and it looked like the end for Wigan as they trailed 30-6.
But Trent Barrett started to exert his influence for Wigan and they were given a glimmer of hope when Calderwood went over for his first try after 55 minutes, converted by Richards.
With both Solomona and Terry Newton off the field and Chris Feather on his way to hospital with a dislocated shoulder, the Bulls were starting to struggle.
Calderwood raced over for his second try and Richards again added the extras before Harrison Hansen's try and another Richards goal cut the gap to six points.
Calderwood sealed his hat-trick when he raced almost the entire length of the pitch with seven minutes left to play to score with Richards levelling up the game.
By now Wigan were looking the hungrier and Richards ensured he had the final say to seal the most remarkable comeback in play-off history.
Wigan coach Brian Noble
"The manner of the last 20 minutes was pretty good from us. Bradford were the better team for the first 60 and I feel for them. They will be kicking themselves.
"At half-time we had a belief we could score three tries. I thought we had thrown the game away, I'll be honest, but we asked them to play for 80 minutes and we finished the game really strong.
"I don't know many teams who could do what we did in the last 25 minutes. We will have to improve next week but there is a huge belief and a huge determination to do very well."
Bradford coach Steve McNamara
"This is as bad as it gets, as tough as it gets. I'm as disappointed as I've been and the boys are a bit bewildered.
"We are obviously hugely disappointed not to get the result because for large parts of the game we dominated. We have learned a harsh lesson tonight.
"Momentum is a huge thing in rugby league and things can change very quickly. Maybe a bit of panic set in and some boys came up with some mistakes."
Bradford: Platt, St Hilaire, B. Harris, Hape, Tupou, Morrison, I. Harris, Vagana, Newton, Lynch, McKenna, Solomona, Burgess.
Replacements: Cook, McAvoy, Feather, Henderson.
Wigan: Richards, Calderwood, Bailey, Vaealiki, Colbon, Barrett, Leuluai, Fielden, Millard, Paleaaesina, Hansen, Fletcher, O'Loughlin.
Replacements: Higham, Hock, Goulding, Prescott.
Referee: S Ganson (St Helens)