The Dutchman went close to notching a second six minutes later when a Hernandez pass put him clear, but his left-foot strike was saved by Felgueiras.
The Reds ended the half on top and began the second in the same fashion and it was the combination of Rooney and van Persie which undid Cluj once again, four minutes after the restart.
Rooney, who was starting alongside van Persie for the first time, floated a lovely ball over the top for the Dutch international who stuck out a boot and flicked the ball home on the volley past the helpless Felgueiras.
They had seen little of the ball up to that point, but Cluj began to rally soon after which, coupled with some shakiness in the United backline, led to a couple of decent openings. After Gabriel Muresan had crossed for Kapetanos to fire over, De Gea reacted brilliantly to tip Cadu’s header, from a Rafael Bastos corner, over the bar.
At the other end, van Persie nearly grabbed his second hat-trick of the campaign on 71 minutes when Rooney, out wide on the left, fired a low cross towards his onrushing strike partner, but he was muscled out of it by a defender and unable to make contact with the ball.
United’s defensive injury curse reared its ugly head as the game ticked towards the final 10 minutes with Jonny Evans unable to continue after