The Eels were humbled 64-4 by the defending champions, who ran in 11 tries at AAMI Park with eight coming in the second half.
Parramatta missed a staggering 53 tackles compared to the Storm's 10. In their defence, they did make 298 against Melbourne's 175.
They have now lost 12 of their past 13 games and are destined to collect their second successive wooden spoon.
Mannah said his team hadn't given up.
"No. I can only speak for myself but no," Mannah said.
"Days like today are very deflating but we've just got to get back on horse and get ready for next week."
Eels coach Ricky Stuart said his team was guilty of school-boy errors and he felt some players "weren't there".
"We were our own worst enemy in that first half, there were errors that you would be critical of it it was your under 16 team.
"The game was riddled with them in the second half.
"I feel sorry for some players out there playing because they didn't deserve that."
Still, Stuart thought their performance didn't warrant such a heavy defeat after only trailing 16-4 at half time.
"Everyone tries and for the amount of effort we probably didn't deserve to get beaten by that but in patches of our game we let ourselves down.
"I'm not taking anything away from the Storm but gee we made it easy in patches."
