Matty Fryatt grabbed the only goal of the game for the Tigers in the 64th minute when he latched onto a long ball from James Chester and slotted a low shot beyond the advancing Lee Camp.
The strike ensured Forest tasted defeat at the City Ground in a regular season match for the first time since September 2009, although they were unfortunate not to claim at least a point from this encounter.
Billy Davies' men carved out the only chances in a largely dour first half and Hull continued to offer little in attack after the interval.
However, Fryatt's clinical finish was to prove the difference as the visitors closed the gap on their opponents to seven points.
Forest slip to fifth in the npower Championship table, although Swansea's surprise defeat at Scunthorpe ensures they remain just three points outside the top two ahead of Cardiff's evening kick-off against Ipswich.
Reds captain Paul McKenna was rested due to a slight knee problem, but left-back Paul Konchesky returned from injury and there were also recalls for Radoslaw Majewski, Paul Anderson and Marcus Tudgay.
Hull were without the services of Brad Guzan following his return to parent club Aston Villa, so Vito Mannone started in goal in the only change to the team beaten 2-0 by Cardiff last weekend.
The hosts twice threatened from corners early on, with Robert Earnshaw heading over from close range following Anderson's neat flick and Majewski seeing a powerful goal-bound shot blocked by Anthony Gerrard.
Earnshaw side-footed wide from 10 yards in the 15th minute following a neat dummy from Tudgay, who tested Mannone with a shot of his own six minutes later.
Hull's goalkeeper was making his first appearance since December following a spell on the sidelines with a thigh injury and appeared to be in some discomfort as the half progressed.
Forest were unable to call the Italian into any further action before the break, however, while home keeper Camp remained a virtual spectator as the Tigers struggled in the final third.
A tame Robert Koren free-kick was comfortably pouched by Camp eight minutes into the second half and Earnshaw saw a set-piece of his own deflect narrowly over moments later.
New loan signing David Amoo was then brought on in place of Jay Simpson for his Hull debut, while veteran midfielder Nick Barmby replaced the hard-working Aaron Mclean.
It wasn't long before the visitors took the lead as Fryatt converted his side's first clear-cut chance from open play.
Forest boss Davies introduced Garath McCleary, Nialle Rodney and Dele Adebola from the bench in an attempt to find an equaliser, but Hull held firm, with Gerrard producing another wonderful block to deny Chris Gunter.
Majewski had a great chance to snatch a point for the Reds with two minutes remaining, only to drag his left-footed shot inches wide.