Former England cricket star Flintoff recovered from a second-round knockdown to claim a debut points victory against limited American novice Richard Dawson over four two-minute rounds at the Manchester Arena.
The 34-year-old's preparations for the bout were charted in a Sky television documentary, causing many in the boxing fraternity to question his motives for stepping into the ring.
Those looking to chastise Flintoff were given further ammunition last night as a crude, scrappy contest predictably developed - not that it seemed too much of a concern for the boisterous 6,000-strong crowd in attendance, who were vocally behind their hero throughout.
Respected former WBA featherweight champion McGuigan, who oversaw the ex-Lancashire all-rounder's painstaking four-and-a-half month training camp alongside son and trainer Shane, had nothing but high praise for Flintoff but turned his fire on critics afterwards.
"We never belittled the sport," he said. "We were never in this, in any way, to belittle boxing. Those who said that were idiots.
"We're in this to show how serious he was about it.
"We never pretended that he was anything other than a novice but we told everyone he was going to give it everything he's got and I think in the fight he showed that.
"He was knocked down, he got up, showed pluck and courage. His technique went out of the window because he wanted to win so much and had the crowd behind him.
"But it was honest. Everything about what we've done over the past four and a half months was honest.
"He's a generous, genuine fella and I think this was a personal battle for him too - he wanted to show that he had the courage to go through with something like this and I think he won that battle."
Flintoff, who conceded his ring bow "wasn't one for the purists", does not expect to dissuade the doubters and fully understands the degree of ill-feeling around a first bout that may also prove to be his last.
"I don't know - they'll probably say I kept dropping my hands," he said when asked how sceptics might have received his gutsy display.
"That's not the reason I did it. I appreciate that people are passionate about sport and people want to protect their sport - I'd be the same with cricket and boxing's no different.
"There's a few who've tried to steal a few headlines, granted, but on the whole people are passionate about sport.
"This whole process was never about degrading boxing. We wanted to do it properly, which we've done.
"We wanted to show boxing for what it is, a fantastic sport, and I wanted to show what boxers go through. Sometimes I don't think they get the credit they deserve.
"I think boxing should be right up there. There's some amazing people and I've seen some amazing things over the past few months."
And Flintoff was quick to pay high credit to the duo who guided him through those experiences.
He added: "The McGuigan name within boxing is massive and I was aware that when I walked out I was carrying that as well.
"I'm just glad that I've come out of there with a win and with that intact because these two guys are the ones who put themselves out there more than I have and I could not thank them enough.
"These are special fellas."