Sam Field grabbed a brace within quarter of an hour during the second half, as the U’s slipped to a fourth defeat in five.
We picked out the key talking points from the match.
Lack of quality in the final third
United managed just one shot on target at Loftus Road, that coming early in the first half when Cameron Brannagan’s effort from outside the box took a slight deflection and flew into the gloves of Paul Nardi.
Midfield trio Brannagan, Idris El Mizouni and Tyler Goodrham worked hard and showed flashes of inspiration, but were unable to create clear opportunities in the final third.
Out wide though, it was a disappointing night for the U’s. Much was made of United’s injury list on the wings, but Matt Phillips and Przemyslaw Placheta have returned to the side in recent weeks.
Phillips got past his marker on a couple of occasions down the right-hand side, but was then wasteful with his crosses against his former club, often overhitting them as if he was trying too hard to silence the smattering of jeers he was getting.
On the left, Placheta failed to get into the game and was too easily shrugged off the ball when he did have possession. Not once was the pace previously demonstrated on show.
All in all, it meant that Mark Harris cut a frustrated figure up front. It was a difficult night to lead the line, and Harris was starved of service from those around him.
January window feels do or die now
The January window was always going to be important for the U’s. But now it seems like it’s going to be crucial to the outcome of the season.
Ben Nelson’s quad injury means centre back cover is probably a necessity, while a flair midfielder capable of producing goals and assists wouldn’t go amiss.
Perhaps more than anything though, it’s out wide where United need fresh legs.
The aforementioned injuries have hampered the U’s, but none of the wingers have so far looked capable of fulfilling the hole left by Josh Murphy.
Murphy meanwhile is now showing his class at Portsmouth, with four goals and four assists to his name.
United must surely be looking to see if a player of his ilk can be found in the January window.
Rustiness at right back
Peter Kioso enjoyed a fine first half, but looked tired in the second period.
He was at fault in the lead-up to the second goal and almost made a costly mistake for a potential Hoops third.
Kioso has been a solid addition for the U’s, but this was his first game back after falling ill while on international duty. United need him fully fit and firing.