Rangers, still without injured top scorer Charlie Austin and still without a win under manager Jimmy Floyd Hasselbaink, seemed to have rescued a point when Sebastian Polter headed in an 86th-minute equaliser to cancel out Abel Hernandez's opener.
However, a mix-up between Rangers defender Grant Hall and goalkeeper Rob Green helped prove the difference, as t he pair collided in attempting to clear Sam Clucas' cross and the ball rebounded off Diomande and into the net
Beaten Rangers find themselves 15th in the Championship table six matches into Hasselbaink's reign, while Hull moved into third place, this after Brighton were beaten by Wolves earlier on Friday evening
In a game low on quality, Polter had a decent chance and Alejandro Faurlin went close for them during a turgid first half.
After Hull's Jake Livermore had given the ball away, striker Polter hesitated and his shot was blocked by Harry Maguire.
Polter was given a starting place by Hasselbaink along with Tjaronn Chery, who sent an early effort over the bar.
Alejandro Faurlin had a firm strike tipped over by Allan McGregor, and at the other end Mo Diame and Ahmed Elmohamady steered shots wide of the target.
QPR struggled to create chances but did go close to taking the lead three minutes before half-time, when Chery's corner was nudged over the bar by Faurlin from close range.
Rangers, whose reliance on Austin was underlined once again, were just as uninspiring after the interval and Hernandez put Hull ahead with a sublime finish on 61 minutes.
Diame found space on the left and picked out the Uruguayan striker, who steered a calm first-time shot beyond Green for his 10th league goal of the season.
The best Rangers could muster was Paul Konchesky's left-footed shot into the side-netting, before the 78th-minute introduction of Jamie Mackie at least raised the home fans' spirits.
Mackie, back in action after more than three months out with a hamstring injury, gave them some much needed impetus up front.
German striker Polter had struggled to make an impact up front before netting his second goal in as many matches to haul the hosts level.
Matt Phillips delivered a perfect cross from the left and McGregor got a hand to Polter's header but could not keep it out of the net.
The game looked to be heading towards a draw before Clucas' cross from the left wing caused trouble for the QPR defence, with Diomande the happy recipient of an unexpected rebound.
Source : PA
Source: PA