Harlequins slumped to a second straight Super League loss as struggling Huddersfield completed the double against the Londoners.
After a disastrous run of games, which has seen the Giants win just one of their last seven matches, Huddersfield roared back to form, scoring four tries as they hauled themselves away from the drop zone.
Quins created the first opening after four minutes, seizing on a mistake in the Giants midfield but Tyrone Smith was unable to gather Danny Orr's pass.
Giants took the lead in the 10th minute, Chris Nero breaking clear and running the ball home from 45 metres against the run of the play. Skipper Chris Thorman converted.
Quins winger Jon Wells was inches away from catching a hopeful cross-field kick from Scott Hill before retiring with a neck injury he picked up in the second minute.
Both sides wasted good possession with handling errors before Quins upped the pressure in the 10 minutes before the break.
Orr and Smith were both held up just short of the try line before Louie McCarthy-Scarsbrook converted a Julian Rinaldi pass in the 37th minute. Paul Sykes levelled matters with his conversion.
The Giants camped in the Quins 22 at the start of the second half and they were rewarded when Nero broke two tackles and crossed the line in the 45th minute for his second touchdown of the game.
The pressure did not relent and seven minutes later, Steve Snitch ran in the Giants' third try of the game. Thorman converted from in front of the posts to make it 16-6.
The Giants kept the Quins defence under pressure with clever, probing kicks to the corners from Thorman and Robbie Paul.
But Quins hauled themselves back into the game when Sykes went over in the corner after 62 minutes.
The Giants restored their lead on 68 minutes when a delightful sidestep from Kevin Brown wrong-footed the Quins defence and allowed him to score under the post. Thorman's conversion made the score 22-10.
Concerted late pressure from the home side failed to bring a breakthrough as handling became more difficult during a torrential downpour, allowing the Giants to complete a league double.