|Huddersfield (8) 22|
|Tries: Lawrence, Symonds, McGillvary 2 Goals: Ellis 3|
|Hull FC (0) 12|
|Tries: Washbrook, Fonua Goals: Sneyd 2|
Jermaine McGillvary scored two tries to keep Huddersfield's fading Super League top eight hopes alive and hand a first defeat in 11 to leaders Hull FC.
Having led 8-0 at half-time, three tries to two after the break sealed it.
Giants are four points adrift of a Super 8s place with three games of the regular season to play, although they need other results to go their way.
Hull stay top, two points clear of Wigan, who play fourth-placed Catalans Dragons on Saturday.
Lee Radford's side were firm favourites to continue their fine form but a Giants side potentially playing under interim head coach Andy Kelly for the final time, showed aggression and hard-running to unsettle the visitors.
Jake Connor, a player bound for the Black and Whites next season, proved a pivotal figure with his running, smart hands and notably his kicking game.
They went ahead when Jamie Ellis screwed a dangerous kick behind the Hull line that Michael Lawrence chased down to score, and Ellis' penalty in the last moments of the half extended their lead.
Seven times Hull had trailed at the break this season, going on to reverse the deficit to win in four of them, and they looked like they might repeat that feat when Danny Washbrook rumbled across on the back of a penalty to get the visitors on the board.
The fightback was snuffed out when Symonds raced onto another Ellis tester to push the Giants' lead out to 14-6, and twice they got the ball wide to McGillvary with smart hands to take his tally of career tries to 150.
Mahe Fonua reduced the deficit when he crossed but Huddersfield held on to record back-to-back league wins for the first time this season.
Huddersfield interim head coach Andy Kelly told BBC Radio Leeds:
"It feels good, it feels good for the players who have copped a lot of flak after the Wakefield defeat.
"We talked about honesty and trust and building respect back for each other and the players were really open minded about what they wanted to do to achieve that.
"They went out there and expressed themselves, the youngsters matched the older guys and worked to fill the gaps and the senior players led from the front."
Hull FC head coach Lee Radford told BBC Radio Humberside:
"The score flattered us, we spoke about how predictive we were on our shifts.
"After we got back to 8-6 we got schooled in how to play wet weather rugby, absolutely clinical in putting the goal in the in foal and making us make tackle after tackle.
"I have to question the patience we didn't show, their halves' game management was absolutely superb.
"This weather is Grand Final weather and if you're not prepared to show patience at that time of the year there are no rings on anyone's fingers."
Huddersfield: Connor; McGillvary, Cudjoe, S. Wood, Murphy; Ellis, Brierley; Rapira, Leeming, Ta'ai, Symonds, Lawrence, Hinchcliffe.
Replacements: Crabtree, K. Wood, Mason, Roberts.
Hull: Naughton; Michaels, Fonua, Tuimavave, Talanoa; Pryce, Sneyd, Taylor, Houghton, Green, Manu, Minichiello, Pritchard.
Replacements: Thompson, Hadley, Bowden, Washbrook.
Referee: Chris Kendall (RFL)