Harper; Simpson, S Taylor, Khizanishvili, Enrique; Guthrie (Lovenkrands, 88), Smith, Nolan, Butt (Gutierrez, 46); Ranger (Harewood, 61), Carroll.
Subs not used: Krul, Kadar, Donaldson, Geremi.
The on-loan Aston Villa striker poked home Andy Carroll's 70th-minute header to cancel out Ben Watson's early opener and increase the Magpies' lead at the top of the table to three points.
The crowd of 38,923 was 4,000 down on the visit by Plymouth last week, which takes some explaining following the superb win at Ipswich last week.
United didn't start very well, and the pace of winger Wayne Routledge and the movement of midfielder Ben Watson troubled the Magpies all night.
Danny Guthrie had a first-half penalty saved by Radek Cerny and Carroll and Kevin Nolan both went close with headers.
QPR took the lead with just seven minutes gone when Jose Enrique's poor clearance fell to Watson, who made ground to the edge of the box and fired home with the help of a deflection off Steven Taylor.
Newcastle should have been back on level terms with 19 minutes gone when defender Damion Stewart was penalised for handball in the box as he blocked Taylor's shot.
However, Guthrie's spot-kick was not well hit or placed and Cerny guessed correctly and saved comfortably as he dived to his right.
Guthrie passed up another opportunity 13 minutes before the break when, after being played in by Danny Simpson, he shot at Cerny from a tight angle when he perhaps should have squared for Carroll.
At last, the QPR goal was coming under sustained pressure and Gary Borrowdale had to hack a 33rd-minute Carroll header off the line before Nolan directed another effort at the keeper seconds later.
Caretaker boss Chris Hughton replaced skipper Nicky Butt with winger Jonas Gutierrez, back from a hamstring injury, at the break in an effort to inject some pace into his side, but it might have been 2-0 within three minutes of the restart.
Vine did well to get in a cross from the right after Harper had punched a corner away, and Stewart powered a header just wide of the post.
Newcastle responded in determined fashion, but were almost hit on the break with 59 minutes gone when Vine fired wide of Harper's right post after working his way into a promising position.
Carroll drove a 66th-minute free-kick straight at the keeper as the Magpies pressed once again, and he played a major role in the equaliser four minutes later, heading down Simpson's cross for Harewood to stab home at the far post.
The striker turned a 79th-minute Gutierrez cross across the face of goal, but Newcastle had to make do with a point on a frustrating night.