Latics, with nine changes from the weekend, suffered their first defeat in all competitions since their opening-day league loss at Sunderland in convincing fashion.
A Sunderland side with eight changes of their own bossed the game from virtually the first whistle.
And a goal in either half from Nathan Broadhead and Luke O'Nien saw the visitors deservedly book their place in the last 16.
"First and foremost, that certainly wasn't the result we wanted," recognised the Latics boss.
"But on the flip side, there were a lot of lads who needed 90 minutes, and the bench was full of academy graduates.
"It was important that the likes of Gavin Massey, Gwion Edwards and Stephen Humphrys got minutes.
"We know the campaign is going to be so tough, with so many three-game weeks on the way.
"We need as many lads up to speed in terms of match minutes, sharpness and decision making, and there's no better way to do that than a very competitive game."
One positive was a debut for centre-half Jason Kerr, who arrived from St Johnstone on deadline day.
"Jason's obviously not played for us, he came down with a bit of an ankle injury," said Richardson.
"It was important for him to make his debut, to get to know a few people out there on the pitch, and how he can fit in.
"It'll be good to sit down with him now he's made his debut and get some more information into him."
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