Anthony Seibold feels Manly "killed" themselves as they fell to Cronulla 30-14 on Sunday afternoon.
A lacklustre first half saw the home side go to the sheds down 14-0 to the Sharks.
To their credit, the Sea Eagles fought hard to level things by the 61st minute, with Tolutau Koula bagging a double.
However, moments later, they again found themselves on the back foot, as some sloppy defence saw Braydon Trindall snatch a try.
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This opened the floodgates somewhat, and Cronulla scored a further pair of tries to claim a strong win.
Seibold was particularly disappointed by his team's errors.
Manly made 15 mistakes compared to their opponent's 11.
He noted how the constant concession of field position cost them dearly.
"Back end of the game, we just killed ourselves with errors," Sea Eagles coach Seibold said.
"Across the whole game, we killed ourselves with errors.
"We turned over the footy down our end of the field and they were good enough to capitalise a number of times.
"We put a lot of pressure on ourselves with field position. We just weren’t good enough to get the job done tonight.
"We need to be better, there’s no doubt about it.
"Our defence dropped off at the back-end of the game, and we didn’t get another chance.
"It’s obviously frustrating for us internally, and our supporters as well."
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Considering they were fresh off a bye, Sunday's defeat was particularly disappointing for Manly.
The 8th-placed outfit will aim to bounce back next week when they head north to play the Cowboys.