Robin van Persie scored twice as Manchester United came from behind to take a significant step towards the last 16 of the Champions League.
The Dutchman scored either side of half-time to help United recover their poise having fallen behind to Pantelis Kapetanos's 14th-minute opener.
Van Persie's equaliser had more than an element of luck about it, the ball looping into the net off his shoulder.
Landmark night for United
This was United's 100th win in the Champions League, equalling Real Madrid's record, Barcelona are on 99
This was the first time United have won their opening two group since matches 2009-10 and only the fourth time in the last 10 seasons
Robin van Persie has now scored seven goals for United in all competitions this season, more than any other Premier League-based player
His winner was delightful, however, as he flicked in Wayne Rooney's pass.
While Sir Alex Ferguson had the luxury of starting with Van Persie and Rooney together, this victory over the Romanian champions was far from vintage.
But United did not have to operate at full capacity as Cluj, having showed glimpses of promise before half-time, faded badly in the second half before Van Persie's sixth and seventh goals for the club took the visitors top of Group H.
The Premier League side had looked the more vulnerable in the opening stages, with Rio Ferdinand and Jonny Evans continuing to struggle in defence, but they worked hard to find their rhythm and eventually saw out the tie with a measure of control that had looked unlikely in the opening 20 minutes.
Two matches against Braga of Portugal should now see United avoid a repeat of last year's failure to qualify from the group.
The 3-2 defeat by Spurs at Old Trafford on Saturday had been the fifth time in six Premier League games United had fallen behind. Ferguson insisted United would not suffer a similar fate in Europe, Cbut luj were ahead after 14 minutes.
They took full advantage of United's growing susceptibility to the swift counter attack with Modou Sougo surging beyond Patrice Evra and crossing low for Kapetanos to evade Jonny Evans and steer his first-time shot beyond David De Gea.
Sougo continued to torment Evra down the right and the hamstring injury that forced the Senegal winger to limp off nine minutes after the goal robbed the Romanian side off their most potent attacking threat.
United's alarming lack of width was undermining their obvious attacking intent. For much of the first half, they looked a team lacking cohesion, confidence and sustained threat; insipid not inventive. After their poor recent form, Ferguson had demanded tempo, instead United were producing tedium.
Opportunities did fall to Rooney, Van Persie and Anderson as United warmed to the task but the manner of the equaliser had more than an element of good fortune.
Van Persie applied the finishing touch but although the Dutchman rose to head Rooney's curling free-kick from wide on the left, it was his shoulder that applied the decisive touch as the ball looped high over Cluj goalkeeper Mario Felgueiras and into the net.
Danny MillsFootball Analyst
"Manchester United weren't brilliant but they have got through and won the game. With six points, they are in a strong position now. When Sougou was on, United looked frail at the back. Once he went off, they recovered. United were good but not completely convincing up front. Good result, but could do better."
The scrappy nature of the goal was typical of the game. On both sides, the football was muscular and committed but absolutely devoid of finesse. With Cluj going long and United apparently going nowhere, it seemed individualism would be their most likely source of joy.
Van Persie dashed onto Rooney's floated pass and reached the ball a moment ahead of Felgueiras before knocking it beyond the goalkeeper with an impudent flick of his left boot.
United found their swagger to produce some typically eloquent attacking moves but although Cluj faded, Cadu's powerful header forced De Gea to tip over, while the Spanish goalkeeper then had to be at his best to deny Bastos, turning the Brazilian's diving header around the post.
United were unfortunate not to win a penalty when Evra was bundled over in the penalty area late on but in the end it made no difference.
Substitution Scott Wootton joins the action as a substitute, replacing Jonathan Evans.
Foul by Dos Santos Luis Alberto on Darren Fletcher, free kick awarded.
Oliveira Anderson challenges Matias Aguirregaray unfairly and gives away a free kick. Matias Aguirregaray restarts play with the free kick.
The ball is delivered by Wayne Rooney, Ricardo Cadu makes a clearance.
Matias Aguirregaray challenges Oliveira Anderson unfairly and gives away a free kick. Robin van Persie takes the free kick.
Unfair challenge on Wayne Rooney by Dos Santos Luis Alberto results in a free kick. Rio Ferdinand takes the direct free kick.
The assistant referee signals for offside against Javier Hernandez. Ricardo Cadu takes the free kick.
The ball is crossed by Oliveira Anderson.
The ball is sent over by Robin van Persie.
Mario Camora produces a cross, save made by David De Gea.
Free kick taken by Daniel Ivo Pinto.
Substitution Sasa Bjelanovic is brought on as a substitute for Pantelis Kapetanos.
Tom Cleverley gives away a free kick for an unfair challenge on Matias Aguirregaray.
Free kick awarded for an unfair challenge on Rio Ferdinand by Rafael Bastos. Rafael Da Silva takes the direct free kick.
Outswinging corner taken from the right by-line by Rafael Bastos, Corner taken right-footed by Rafael Bastos from the right by-line, free kick awarded for a foul by Ionut Rada on Rio Ferdinand. Free kick taken by David De Gea. Ricardo Cadu takes a shot. Save by David De Gea.
The ball is crossed by Robin van Persie, Laszlo Sepsi gets a block in.
Unfair challenge on Patrice Evra by Matias Aguirregaray results in a free kick. Patrice Evra restarts play with the free kick.
Corner taken by Rafael Bastos from the right by-line.
Corner taken right-footed by Rafael Bastos. Corner taken right-footed by Rafael Bastos from the right by-line, free kick awarded for an unfair challenge on Rio Ferdinand by Ionut Rada. David De Gea takes the free kick.
Free kick awarded for a foul by Jonathan Evans on Ionut Rada. Ionut Rada takes the direct free kick.
The assistant referee flags for offside against Javier Hernandez. Jorge Mario Felgueiras takes the free kick.
Free kick awarded for an unfair challenge on Ricardo Cadu by Javier Hernandez. Ricardo Cadu takes the direct free kick.
Shot from deep inside the area by Rafael Bastos goes over the bar.
The assist for the goal came from Wayne Rooney.
48:34 Goal scored
Goal - Robin van Persie - Cluj-Nap'a 1 - 2 Man Utd A goal is scored by Robin van Persie from deep inside the penalty box to the bottom left corner of the goal. CFR Cluj-Napoca 1-2 Man Utd.
Wayne Rooney crosses the ball,
Inswinging corner taken left-footed by Robin van Persie, Daniel Ivo Pinto makes a clearance. Oliveira Anderson takes a shot from just inside the penalty box which clears the bar.
Wayne Rooney takes a shot. Ionut Rada gets a block in.
The game restarts for the second half.
45:00 +1:03 Half time
Half Time The match has reached half-time.
Robin van Persie fouled by Rafael Bastos, the ref awards a free kick. Wayne Rooney produces a strike on goal direct from the free kick, save by Jorge Mario Felgueiras.
The ball is crossed by Rafael Da Silva, Header by Wayne Rooney from deep inside the penalty area misses to the left of the goal.
Shot from long distance by Gabriel Muresan goes wide of the left-hand upright.
Corner taken right-footed by Wayne Rooney from the left by-line, Laszlo Sepsi makes a clearance.
Centre by Rafael Da Silva.
Free kick awarded for an unfair challenge on Tom Cleverley by Matias Aguirregaray. Tom Cleverley takes the free kick.
The ball is crossed by Rafael Bastos, Oliveira Anderson gets a block in.
The ball is swung over by Patrice Evra, blocked by Daniel Ivo Pinto. Inswinging corner taken right-footed by Wayne Rooney from the left by-line, Robin van Persie gives away a free kick for an unfair challenge on Laszlo Sepsi. Jorge Mario Felgueiras takes the direct free kick.
Robin van Persie takes a shot. Save by Jorge Mario Felgueiras. Wayne Rooney has an effort at goal from outside the box which goes wide right of the target.
Laszlo Sepsi sends in a cross.
Javier Hernandez takes a shot. Save by Jorge Mario Felgueiras.
Wayne Rooney provided the assist for the goal.
28:40 Goal scored
Goal - Robin van Persie - Cluj-Nap'a 1 - 1 Man Utd Robin van Persie fires in a goal from inside the area high into the middle of the goal. CFR Cluj-Napoca 1-1 Man Utd.
Foul by Ricardo Cadu on Javier Hernandez, free kick awarded. The ball is crossed by Wayne Rooney,
The ball is sent over by Robin van Persie, clearance made by Ionut Rada.
Substitution Moudou Sougou leaves the field to be replaced by Dos Santos Luis Alberto.
Robin van Persie produces a left-footed shot from deep inside the penalty box which goes wide of the left-hand post.
Free kick awarded for a foul by Patrice Evra on Moudou Sougou. Direct free kick taken by Gabriel Muresan.
Shot from just outside the penalty box by Oliveira Anderson misses to the left of the target.
Robin van Persie takes a inswinging corner to the near post, Rio Ferdinand takes a shot. Save by Jorge Mario Felgueiras.
Wayne Rooney takes a shot. Jorge Mario Felgueiras makes a save.
Gabriel Muresan concedes a free kick for a foul on Robin van Persie. Direct free kick taken by Rafael Da Silva.
Wayne Rooney takes a inswinging corner from the left by-line played to the near post, Ricardo Cadu manages to make a clearance. Wayne Rooney delivers the ball, save made by Jorge Mario Felgueiras.
Robin van Persie sends in a cross, Ionut Rada manages to make a clearance.
Unfair challenge on Robin van Persie by Daniel Ivo Pinto results in a free kick. Free kick taken by Rafael Da Silva.
Assist by Moudou Sougou.
13:10 Goal scored
Goal - Pantelis Kapetanos - Cluj-Nap'a 1 - 0 Man Utd Pantelis Kapetanos scores a goal from deep inside the penalty box to the bottom left corner of the goal. CFR Cluj-Napoca 1-0 Man Utd.
Moudou Sougou delivers the ball,
Robin van Persie concedes a free kick for a foul on Matias Aguirregaray. Free kick taken by Moudou Sougou.
Oliveira Anderson has shot on goal from just outside the box which goes wide of the right-hand upright.
Javier Hernandez crosses the ball, Ionut Rada makes a clearance.
Moudou Sougou takes a shot. Blocked by Jonathan Evans.
Mario Camora sends in a cross, Rio Ferdinand makes a clearance.
Rafael Bastos takes a inswinging corner.
Mario Camora crosses the ball, blocked by Rio Ferdinand. Corner taken by Rafael Bastos from the left by-line, Moudou Sougou takes a shot. Clearance made by Jonathan Evans.
The match has kicked off.
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