The Romanian champions held on to condemn Sir Alex Ferguson to his 39th defeat in his 200th European Cup match as United boss, and his third in United's past five European home games. However, Luis Alberto's magnificent second-half strike still was not enough for Cluj to join United in the last 16.
In making 10 changes from the side which won at Reading on Saturday, Ferguson seemed to be offering three, at the very most four, a chance of being involved in Sunday's Manchester derby.
And one of them, Chris Smalling, did not do much to convince he could stop the 'Cartoon Cavalcade' defending United's manager accused his team of at the Madejski Stadium with a poor clearance to Rafael Bastos, which was followed by the England man nearly deflecting the subsequent shot into his own net.
United finally shook off their lethargy six minutes before the break when Danny Welbeck met Wayne Rooney's corner at the near-post, only to be denied in unorthodox fashion by Mario Felgueiras, who somehow managed to keep the header out. Felgueiras' agility was on show again moments later as he clawed Rooney's deft chip out of the top corner.
Ferguson's hope of escaping the evening unscathed given Sunday's crucial trip to the Etihad Stadium was dashed just before the break when Tom Cleverley headed straight for the dressing rooms after being replaced by Paul Scholes.
Of course, whilst this fixture was reduced to the status of the last game to be ticked off before the really big one four weeks ago, when United confirmed themselves as group winners and a seeded team in the last-16 draw later this month, for Cluj there was plenty to play for.
And a small, but noisy contingent from Romania were given something to warm them up 11 minutes after the re-start when Luis Alberto scored a beauty, his 30-yard shot curling away from the returning David de Gea and into the top corner.
Rooney remained on the periphery until he became the unwitting villain in Cluj eyes for failing to turn the ball out of play after Rui Pedro had taken a knock. Green shirts berated Rooney for an age, with Italian referee Daniele Orsato doing little to stop them.
Wisely though, the striker kept his cool and it was Rooney who set up Phil Jones from an acute angle, although Felgueiras was equal to his effort. They didn't know it. But all this effort was in vain for the visitors, who were being turfed out of the competition by Galatasaray's comeback in Braga.
Source: PA
Source: PA