After a quiet start, Ronaldo suddenly sprung to life after the hour, arriving with perfect timing to head in Wes Brown's looping cross.
It was Ronaldo's first goal of a campaign that has already been shortened by a three-match ban imposed for his dismissal at Portsmouth last month.
"He scored 23 goals last season and it is absolutely realistic that he could at least achieve that again," Ferguson said.
"We expect him to improve as a footballer. We expect to see the development in his football.
"He has two great feet, he is marvellous in the air and there is no reason why he can't do even better than he did last year."
After spending seven of his formative years at Sporting, the home fans have clearly not lost their affection for the Madeira-born star.
He was afforded a standing ovation when he was replaced by Carlos Tevez four minutes from time.
"That is a rarity in modern football," observed Ferguson.
"Cristiano is obviously one of their former players and it probably reflects how grateful they are to have nurtured such an incredible young talent.
"Sporting developed him for seven years, now we are fortunate to have him for what we hope will be the best years of his life."
