It was a tall order to improve the most devastating attacking team in European football but then tall orders are what Sir Alex Ferguson specialises in.

Last night Dimitar Berbatov and Wayne Rooney were miles ahead of anything Celtic had to offer and the Scottish champions got off lightly. Others, you fear, might not be so lucky.

Berbatov's two goals made it six in four for the £30.75m man, Rooney's strike 14 minutes from time was his ninth in seven games for club and country. Gordon Strachan may have said that this week that his team were dwarfs in terms of their stature; a less kind description would have them as pygmies in the face of a team currently laying waste to everything in their path.

All this without a performance that was not anywhere near his best from Cristiano Ronaldo. Remember him? There was a lot more pouting from the whinging winger who seemed to take little joy in his contribution to Berbatov's second goal. He trudged off slowly nine minutes from time, playing up his glum mood. Perhaps he is trying to tell us something. But when United are playing this well without him starring no one seemed to care.

In their yellow and green away strip, Celtic resembled Norwich City and at times they looked about as effective. It will no doubt be better when they face United at Celtic Park on 5 November but all the old realities about the gulf in class between English football and its Scottish neighbour were writ large last night. Nowhere more so than in the performance of Rooney who was at the centre of everything good about United again.

If Gordon Strachan had tried to decipher Sir Alex Ferguson's line-up from his words yesterday then he would have been better off taking the advice of seasoned Ferguson watchers. Ferguson may have talked down Ronaldo's confidence and agonised over his fitness but that never constituted a guarantee that the player himself would not be playing.

Ronaldo started for United last night and those who thought otherwise were reminded of that wisdom Ferguson once offered on those who would try to predict his team selections: "Never try to read the mind of a madman". There did not look like there was much wrong with Ronaldo's fitness even if, for periods of the game, he did not seem to be enjoying himself much.

After some early gains in which United pressed Celtic's left side, and the full-back Lee Naylor, relentlessly, Ronaldo did go a little quiet in the first half. It was telling that eventually United's opening goal was to come from a corner earned from a move down their left wing. Ronaldo's mood may have been altered, according to Ferguson, by his slow recovery from ankle surgery but he still looks much the same in one key way: he is desperate to be centre of attention.

That meant a lot of huffing and puffing when his occasional attempts on goal were unsuccessful, the best of which, in the early stages, was when Berbatov flicked the ball out right and Ronaldo smashed it wide. He played up to the cameras after that miss but later his lazy ball meant for Gary Neville was cut out and Ronaldo was embarrassed enough to chase back and cover for the right-back.

United were without Rio Ferdinand too – his groin injury meant a start to Jonny Evans – which, with Wes Brown on the bench, left Nemanja Vidic as the only one of Ferguson's first-choice back four among the starters last night. Celtic struggled to emerge from under United's heel for much of the first half although they did have their chances. Gary Caldwell's shot was tipped over by Edwin van der Sar on 19 minutes.

The song celebrating Ronaldo's triumph over England at the World Cup finals of 2006 is still conspicuous by its absence at Old Trafford – instead the love is reserved for Rooney who was the busiest of United's attacking players in the first half. He connected beautifully with Luis Nani's cross on 18 minutes but had his volley blocked by Glenn Loovens in the Celtic area.

United's goal came just before the half hour, a muddle in the Celtic area as the Scottish side became increasingly ground down by the relentless waves of attacks. Nani won a corner on Celtic's right side which he crossed over – it was half-cleared and came back in via John O'Shea and Naylor to Berbatov. He applied just the faintest of touches to steer it past Artur Boruc from close range. United should have had a second when Darren Fletcher shot over at the end of the first half.

There was a suspicion of offside about Berbatov's first goal and hint of it about his second too which, in its execution, was even simpler. Scott Brown conceded a free-kick to Anderson on the edge of the area and Ronaldo's shot looked to be going wide when Boruc disastrously parried it back into the six-yard box. Berbatov could have walked it in.

Two goals ahead and this had become a stroll for United, who should have had a third minutes later when Ronaldo played in Rooney and he was wrongly flagged offside before beating the goalkeeper. After the goal he was wrongly denied against West Bromwich Albion on Saturday, that was another he could feel rueful about.

Rooney's goal was a move that stretched from box to box. Van der Sar rolled the ball out to Fletcher, he carried it forward and found the substitute Carlos Tevez. He cut in from the right and found Rooney on the edge of the box, who twisted and turned before he made the space to angle a shot across Boruc's goal and into bottom left-hand corner. Rooney has now scored in United's last five games.

After a blow to the right ankle on which he had an operation this summer, Ronaldo took his leave before the end of the game. Old Trafford has still not made their mind up how to treat this errant son but they are certainly no longer as madly in love with him as before the events of the summer. So far they are top of Group E and progressing quite nicely with the players who once made up Ronaldo's supporting cast.

Manchester United (4-4-2): Van der Sar; Neville (Brown, 60), Evans, Vidic, O'Shea; Ronaldo (Park, 82), Fletcher, Anderson, Nani; Berbatov (Tevez, 60), Rooney. Substitutes not used: Kuszczak (gk), Giggs, R Da Silva, Gibson.

Celtic (4-2-3-1): Boruc; Wilson, Loovens, McManus, Naylor; Brown, Robson (Maloney, 61); Nakamura (Hartley, 61), Caldwell, McGeady; McDonald (Sheridan, 77). Substitutes not used: Brown (gk), Hinkel, Donati, O'Dea.

Referee: F De Bleeckere (Belgium).

*Substitute Joseba Llorente came off the bench to score a hat-trick and help Villarreal see off Aab Aalborg 6-3 in Group E last night. The Danes started brightly and struck first when Marek Saganowski headed their first goal of the competition. Giuseppe Rossi and Joan Capdevila then struck within five minutes of each other for the home side, but it was 2-2 at halftime after Thomas Enevoldsen levelled. Llorente appeared midway through the second half and scored twice in three minutes to put the 2006 semi-finalists in command, but Andreas Johansson pulled one back, and it required late goals from Robert Pires and Llorente to seal victory.