On scoring the goal that defeated Sporting Lisbon on his return to the Estádio José Alvalade in September, Cristiano Ronaldo suppressed his instinctive glee and bowed respectfully to the supporters who saw him take the first steps in his professional career. Back in his Old Trafford realm last night, having eliminated them from the Champions League with a spectacular stoppage-time free kick, he did what came naturally, offering a self-satisfied shrug that told his former team-mates it was nothing personal, just a genius going about his business.

It was a moment that evoked memories of two of Ronaldo’s predecessors in the Manchester United No 7 shirt. If the execution was worthy of David Beckham, the celebration was pure Eric Cantona. Like them, Ronaldo exhibits a sense of theatre in the way he composes himself, inviting the gaze of the entire crowd before stepping forward to strike a free kick. When he misses, it can look preposterous, but when he is on target, it is tempting to wonder whether there is a more devastating talent in football.

Ronaldo is not perfect. Here, as has often been the case this season, his performance was punctuated by moments of self-indulgence, but it will always be thus with a player whose first instinct is often to showcase his talent.

What has changed since he left Sporting as an 18-year-old in 2003 is his end-product. Even if he is not performing with the consistency he showed last season, this was his eleventh goal of the campaign and his ninth in his past eight matches. It was also his fifth of the season in the Champions League.

His late intervention was hardly one to underline United’s credentials in the tournament — they had needed what looked like an own goal from Marián Had to cancel out Abel’s spectacular strike midway through the first half — but, thanks to Ronaldo, they secured first place in group F and thus, so the theory goes, an easier draw in the last 16.

As Sir Alex Ferguson noted afterwards, winning the group also affords him the luxury of a clear conscience as he rests players for the trip to AS Roma on December 12, which is now a dead rubber, before the more important Barclays Premier League match away to Liverpool four days later.

United deserve that luxury as the only remaining team with a 100 per cent Champions League record, but this was not one of their better nights. Darren Fletcher, as is his wont, incurred the wrath of the crowd on a couple of occasions before departing at half-time, but far more disturbing were the performances of Michael Carrick, who lacked the assertiveness he developed over the course of last season, and Louis Saha, who offered another bewilderingly poor performance in attack. Ferguson spoke up for Saha, citing his lack of match fitness, but it was a display that will have done little to banish the misgivings that the manager has held about the France forward over the past 12 months.

With United below par, there was an opportunity for Sporting’s outstanding young prospects, notably the coveted Miguel Veloso and João Moutinho, to exhibit their talents, but it was Abel, the unheralded full back, who will most cherish his trip to Old Trafford.

Ferguson called it a “freak of a goal” and then suggested he would have to “see it again”. Indeed he will, for it was not the fluke that the United manager seemed to imply. From his position near the right-hand touchline, Abel might have been expected to cross the ball, but the manner in which he beat Tomasz Kuszczak with a fierce, swerving shot that flew inside the near post was the result of improvisation and technique rather than mere luck.

Sporting could have been 2-0 up soon afterwards, with Liedson the unfortunate victim of a marginal offside decision after more hesitant United defending, but after the half-time introduction of Ryan Giggs and Carlos Tévez, United gradually roused from their slumber.

Tévez supplied a much-needed urgency alongside Saha, but he was pushing his luck when he claimed the equaliser, with Ronaldo’s scuffed shot seemingly turned in by Had. It was enough to convince Uefa, who immediately credited the Argentinian with the goal, but the record books may eventually be amended to show an own goal by the Slovakian defender.

Inevitably, though, it was Ronaldo who had the last word, striking the ball past Rui Patrício from 25 yards after a foul on Anderson. “The boy owes a lot to Sporting,” Ferguson said afterwards. Over the course of this Champions League campaign, though, he has been a source of misery to them as well as undoubted pride.