Latics trailed to Danny Andrew's early free-kick, and Fleetwood doubled their advantage within seven minutes of the restart when Callum Morton netted from the penalty spot.
But three goals in the space of 10 minutes after the hour mark - from Callum Lang, Will Keane and Curtis Tilt - saw Latics record their first midweek victory of the season at the 10th attempt.
"The result is obviously fantastic," acknowledged Richardson. "I actually thought we finished the end of the first half with great momentum, and I felt if we got something we'd go on and win it.
"Was their first goal a free kick...(no)...should Callum Lang have had a penalty? Absolutely.
"But great credit to the lads, they kept going and they kept believing.
"And when you have that kind of character, and go right to the end, you normally get what you deserve.
"Whether there was a bit of luck involved...I just think the character and the endeavour allowed us to get the result."
Richardson's decision after Fleetwood's second goal send on Gwion Edwards for Jason Kerr - and revert to a 4-2-3-1 formation - changed the course of the game.
But the manager felt his side were already on the right track.
"When you get into the right areas, and you make the right decision, rather than playing with emotions, these things happen," he said.
"Even at 2-0 down, I didn't feel we were snatching at things, or getting carried away with the state of the game.
"It remained about our habits, and making sure when the chances did come, we were clinical enough to take care of them.
"We put more than enough balls into the box to get something and, on the balance of the whole game, we deserved it."
Latics have now won a club-record six away matches on the spin, ahead of an 18-day 'rest' in the league because of the FA Cup and the international break.
"Credit goes to the players and the extended staff, and also the players who maybe haven't been involved as much," added Richardson.
"I thought Gwion Edwards was fantastic when he came on, he didn't just maintain his level, he took it up a notch, and that's what you want.
"We want any of the players who come into the side to be able to input themselves on the game.
"The focus is still on us to improve and be even better - individually, collectively and as a club.
"We know where we want to get to in the football pyramid as Wigan Athletic, and we're not there yet.
"There's a lot more to come, and that involves a lot more hard work yet."
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