The inability to break through a compact QPR side means the champions are four points behind United, which can surge seven points clear by beating Southampton on Wednesday.
"We are disappointed for this result," City manager Roberto Mancini said. "We had our chances to win, and we dominated the game, but QPR defended very well, got players behind the ball. We lost two points, for sure."
QPR remains bottom, but is now three points behind Reading and four adrift of Aston Villa.
Newcastle climbed four points clear of Aston Villa after goals from Papiss Cisse and Yohan Cabaye clinched a 2-1 win at Villa Park that plunged the hosts into the drop zone.
Wigan moved out of the relegation places on goal difference after drawing 2-2 at Stoke, while Swansea drew 0-0 with Sunderland in a meeting of mid-table teams.
At a rain-swept Loftus Road, two of the seven places on the QPR bench were filled by goalkeepers: Rob Green and Brian Murphy, who has made just one appearance for the club.
It was a clear message from manager Harry Redknapp to chairman Tony Fernandes about just how desperate he is for new signings before the transfer window closes on Thursday night.
The third goalkeeper in the matchday squad, Julio Cesar, came under pressure from the start. But in front of him, the defence remained disciplined to thwart waves of attacks.
Cesar was beaten in the 20th minute, but Pablo Zabeleta's diving header crashed against the crossbar and Sergio Aguero missed the target when the rebound reached him.
City was getting closer, with Javi Garcia curling just wide of Cesar's right post, but goalkeeper Joe Hart also had to be alert to deny Adel Taarabt with a fine save.
That block, though, was bettered at the other end by Cesar, who tipped Gareth Barry's effort wide.
The target evaded City after the break, with Aguero firing wide, substitute Edin Dzeko heading over and David Silva's fierce strike after a one-two with Carlos Tevez kept out by Cesar.
City was denied a penalty when Scott Sinclair went down under a challenge from Nedum Onuoha, who appeared to get the ball first.
"It's a bonus point — they rip teams to pieces home and away," Redknapp said. "We will take a point off them any day."
At Villa Park, Newcastle finally halted a run of 17 games without a victory on the road in all competitions this season.
Cisse put Newcastle ahead in the 19th minute, latching onto a pass from new signing Moussa Sissoko and dispatching a low shot past goalkeeper Brad Guzan.
"We have worked really hard on integrating the new players," Newcastle manager Alan Pardew said. "They are not here to save us, they are here to help us."
Newcastle went further ahead in the 31st after Villa captain Ron Vlaar headed a clearance straight to Cabaye, who unleashed a shot on the bounce from just outside the area past the diving Guzan.
Villa couldn't mount a comeback despite Christian Benteke netting a penalty early in the second half after Mathieu Debuchy fouled Gabriel Agbonlahor.
"We paid the price for starting too slowly," Villa manager Paul Lambert said. "We just never got going in the first half. The second half, that's the way to play football."
At the Britannia Stadium, Stoke was cruising after Ryan Shawcross hooked in the opener in the 23rd and Peter Crouch pounced at the start of the second half to score his first goal since September after Charlie Adam's shot was parried by Ali Al Habsi.
But Stoke was denied its first win in five league matches. James McArthur began the fightback in the 50th and Franco Di Santo volleyed in the equalizer in the 61st.