Cristiano Ronaldo's astounding early goal left Sir Alex Ferguson to go head-to-head with old rival Arsene Wenger for a place in the Champions League Final.

The emergence of Chelsea and Liverpool may have taken the edge off battles between Manchester United and Arsenal over the past few years.

But the renewal of hostilities promises to be almost as spectacular as the Ronaldo strike that created it.

The sixth-minute effort was his 20th goal of the season and only his second in the Champions League since completing that astonishing haul of 42 in last year's final in Moscow.

There was certainly no doubting it was worthy of winning any game, and earning United the accolade of becoming the first English team to beat Porto on their own ground.

As almost a side issue, it also keeps the Red Devils on track to win the quintuple in a season they have bounced back at just the right time.

In calling for the spirit of Turin '99, Ferguson also knew if that momentous evening was to be repeated, he would have to go through the agony of being two goals down before a famous victory could be achieved.

Ronaldo however, has his own history book to fill.

A repeat of last season's 42-goal tally was never likely to be repeated in a campaign delayed because of ankle surgery.

But the 24-year-old has still make a significant contribution to United's attempt to land an unprecedented quintuple, even if, like so many of his team-mates, he has looked a little off the pace in recent weeks.

There could have been no better stage to signal his renewed intent.

Apart from his beloved Sporting Lisbon, Ronaldo is roundly jeered when he returns to one of the major clubs in his homeland, Porto being no exception.

They recognise his talent, though, even if no-one expected what followed when Ronaldo collected Anderson's short pass closer to the halfway line than the opposition goal.

Sensing a little trepidation in home ranks, Ronaldo let rip with a shot as brutally powerful as it was audacious in its intent.

Porto keeper Helton did not have a chance of keeping the ball out as it flashed past him to give United the start Ferguson could not have dreamed.

Had Nemanja Vidic been able to keep his close-range effort under the crossbar after John O'Shea had got the faintest of touches to a Ryan Giggs corner just before the interval, the Red Devils would surely have completed their task in half the time allotted.

Unfortunately, the Serbian missed, allowing Porto to nurse plenty of hope during a half-time team-talk delivered by Jose Gomes as banned coach Jesualdo Ferreira apparently watched on TV at a secret location outside the stadium.

After his major blunder last week, Bruno Alves was determined to make amends and threatened Edwin van der Sar's goal on three separate occasions during that opening period.

But this was United at their belligerent best. Their intent showed in the reaction of a normally phlegmatic Dimitar Berbatov to losing possession and, after a public rebuke from his manager last weekend for not doing enough for the team, an apologetic wave of regret from Ronaldo after a misplaced pass.

Just as Vidic spurred the chance of a second immediately before the break, so Berbatov did the same just afterwards when he wriggled his way into the Porto penalty area.

Porto took it as their cue to mount another offensive.

But with Rio Ferdinand back alongside Vidic after his recent groin strain there was an authority about United's defending that had not been in evidence since before they were dismantled by Liverpool five games ago.

There was experience too, with Ryan Giggs and Van der Sar taking just long enough over their set pieces not to incur the wrath of Swiss referee Massimo Busacca while eating up vital seconds.

The introduction of Nani for Berbatov midway through the second period hinted at a strategy of counter-attacking at pace.

It was certainly Porto carrying any threat that did exist and Rolando was too close for comfort with a far post header.

Yet this United were different to what has been almost the shadow side that has existed before now.

And while they did not exactly coast home, the visiting supporters were celebrating victory long before the final whistle confirmed it.

Teams:

FC Porto Helton, Sapunaru (Costa 80), Rolando, Bruno Alves, Cissokho, Lucho Gonzalez (Mariano Gonzalez 31), Fernando, Raul Meireles, Lopez, Hulk, Rodriguez (Farias 64).

Subs Not Used: Nuno, Stepanov, Guarin, Madrid.

Man Utd Van der Sar, O'Shea, Ferdinand, Vidic, Evra, Giggs, Carrick, Anderson (Scholes 78), Rooney, Berbatov (Nani 68), Ronaldo.

Subs Not Used: Foster, Neville, Evans, Tevez, Macheda.

Booked: Vidic, Evra.

Goals: Ronaldo 6.

Agg (2-3)

Att: 50,000

Ref: Massimo Busacca (Switzerland).