Huddersfield piled on the agony for reigning Super League champions St Helens with a tense 28-22 victory at Langtree Park to displace them from third place in the table.
Saints did the double over the Giants during the regular season but the Yorkshiremen got their revenge by twice coming from behind to cement their place in the top four.
Keiron Cunningham's men have now lost all three Super 8s matches since their Challenge Cup semi-final defeat by Leeds and urgently need a dramatic upturn in form if they are to have any hope of retaining their crown.
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Saints made the best start and went in front when prop Kyle Amor powered his way over for his first try after seven minutes.
But the visitors seized control with two tries in five minutes as their direct approach began to find holes in the champions defence.
Saints conceded a 10-metre scrum when full-back Adam Quinlan fumbled Danny Brough's grubber kick and former St Helens scrum-half Jamie Ellis bamboozled the home defence with a jinking run as first receiver to cross for the first try.
A surging run from centre Joe Wardle, fresh from signing a new five-year contract, then set up the position for Brough to get back-row forward Ukuma Ta'ai charging over for a second try.
Brough landed both conversions and slotted a penalty from in front of the posts to stretch his side's lead to 14-6 but gradually Huddersfield relaxed their grip.
Giants full-back Scott Grix fumbled two high kicks to put his side under pressure and referee Richard Silverwood awarded seven successive penalties against the visitors as Saints gained the momentum towards the end of the first half.
Huddersfield were reduced to 12 men when substitute Michael Lawrence was sin-binned following a final team warning by Silverwood and St Helens duly took advantage, with James Roby forcing his way over for their second try, with Luke Walsh kicking his second goal to cut the half-time deficit to just two points.
The Giants were still a man short, however, when they scored their third try three minutes into the second half.
Second rower Joe Wardle picked a superb line to accept Brough's pass and scrambled free from the attempted tackle to touch down.
Brough's fourth goal restored his side's eight-point lead but Saints hit a purple patch to take the lead.
Walsh's long pass created the space for centre Mark Percival to get winger Tom Makinson over for a try on his first appearance since recovering from a broken leg, and Makinson then palmed the ball back from Walsh's kick to the corner for Percival to get stand-off Travis Burns over.
Walsh hit an upright with one conversion attempt and was wide with the other to leave the scores tied at 20-20, but when Brough put a goal-line drop-goal straight into touch, he slotted the penalty to edge his side back in front.
The lead changed hands for a third time on the hour when right winger Jermaine McGillvary finished off a delightful move in which Ellis performed a run-around with second rower Jack Hughes to notch his 19th try of the season.
Brough was off target with the boot for the first time but Huddersfield made sure of the win seven minutes later when Wardle's superb cut-out pass enabled left winger Aaron Murphy to cross for a fifth try.