In a match that failed to reach any real heights, the Dolphins had enough strike to pull away late and win 22-0, leapfrogging them above Cronulla into fourth spot.
The Dolphins' win did come at some cost, with in-form second-rower Connelly Lemuelu limping from the field in the second half with a hamstring injury.
But the story of the night was the Sea Eagles, whose finals hopes are now virtually over after six straight losses.
It was against the Dolphins that the Kieran Foran coaching era began with a bang, piling 52 points on them at Redcliffe back in round five.
But on Friday night the honeymoon period died with a whimper, lacking any real threat in attack and unable to crack the opposition line.
Manly can point to any number of things for the way their season has spiralled, with an injury crisis in the middle and the club's alarming lack of depth exposed.
Luke Brooks' ruptured ACL has also proven costly, with the Sea Eagles having far more attacking sets than the Dolphins but failing to cross even once.
It marked the first time since a 6-0 loss to Eastern Suburbs in 1993 that Manly failed to trouble the scoreboard at their traditional home ground.
"It's been tough going, but we certainly won't roll over and throw it in," Foran said.
"We will grow from this. There are reasons why it's been tough and I haven't liked to use any of those as an excuse.
"But we'll grow out of this period, there'll be a lot of good experience and growth that's been put into into a lot of guys.
"That'll hold us in good stead. I'm a firm believer in that."
Manly best chance came at 8-0 down midway through the second half, when a Reuben Garrick flick pass was called forward as Jason Saab sprinted away to score.
From the next set the Dolphins effectively sealed the match, with Selwyn Cobbo getting the ball down in the corner under intense pressure from impressive fullback Clayton Faulalo.
Kristian Woolf's men then went in again moments later through Jack Bostock, after Jamayne Isaako picked off a Joey Walsh pass at the other end of the field.
Usually one of the most dangerous teams in the competition, the Dolphins' attack was hardly at their best either.
Hamiso Tabuai-Fidow put Isaako over for a late try, while their only other came through Kodi Nikorima in the first half with Tolu Koula in the sin bin.
But crucially their defence held firm, one week after leaking 32 points to Brisbane.
"If you're going to do something in finals, you've got to be able to defend well," Woolf said.
"We should take a lot of confidence out of what we were able to do tonight."
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