Bebe came on for his debut in the Carling Cup tie against Scunthorpe on Wednesday, playing the final 16 minutes of United's 5-2 victory.
His arrival at Old Trafford in August came as a surprise, as he had only joined Vitoria Guimaraes a few weeks earlier and Ferguson had declared that his business was done for the summer.
But the Red Devils manager decided to move for the 20-year-old after being alerted to his enormous potential by a club scout.
And after building up his fitness over the past month, Bebe will now hope that his cameo at Glanford Park marks the start of regular involvement with the first team.
"It was one of those instinctive things, you have a smell about something and you take it," Ferguson told CNN.
"We have a scout in Portugal, where we asked him about this young player playing in the second division in Portugal.
"He'd only played three or four games and our scouts insisted that we should sign him.
"It was a bit of a leap into the dark really, because we hadn't seen him play.
"We sent one of our scouts down. to see him play in the last game before we signed him and then he comes up and says there's something exceptional here, we're maybe seeing something really special, and so we took the gamble.
"So he's joined us but physically, he wasn't ready, hasn't done a proper pre-season, so the last few weeks since he's joined, we've been working on him physically."
With Ferguson absent on Tuesday night at Scunthorpe, it was left to Mike Phelan to give Bebe his debut, and the United assistant boss was impressed with what he saw.
Phelan told MUTV: "The scoreline gave us the opportunity to give Bebe a little look at what Manchester United's all about. I thought he responded very well.
"There were fleeting moments of pace and power, and he got a little bit excited now and again. But it's important that players like him get these opportunities."