From there the Warriors lost their shape, making errors in possession and poor defensive decisions, which allowed Manly guns Daly Cherry-Evans and Tom Trbojevic the freedom of Brookvale.
"At 20-12 we should have walked over the line," said Brown of the second-half flashpoint.
"The error didn't cost us the game but it's how we struggle when momentum and things don't go our way and momentum goes against us.
"You are going have opportunities in games when you put sides in a situation where the scoreboard suggests they are a fair way away, and you don't take them, that happens and it's how you respond to them that makes you a good team.
"Our response to that wasn't great. And then we never touched the ball for a while again."
There was a similar period last week, when the Cowboys came home strong, and several other matches this year. It's not an issue unique to the Warriors, especially with the increased pace of the NRL this season.
It's partly game management, partly inexperience and partly mentality, but needs to be addressed to retain any hope of September football.
"We have got to do that far, far better and respond more positively with our defence when we come up with [things] like the error when we should have scored," said Brown.
The left-edge defence was targeted ruthlessly by Manly on Sunday, with wing Jason Saab grabbing a hat-trick, though the Warriors were also exposed up the middle, when Trbojevic scored a quick first-half double.
Brown also questioned his own decision-making around the spine, with Reece Walsh brought on in the 53rd minute for Wayde Egan, with Nikorima switching to dummy half.
It was a difficult introduction for Walsh on the left edge, as Manly were rampant down the right flank, though the teenager helped to spark the late comeback, with several dynamic plays and his first NRL try.
"I don't know if I am using Reece properly, he's only been with us for three weeks and obviously Manly had a plan for when he was on the field," said Brown.
"I've probably got to take some responsibility, because we came up against a smart coach with some blokes that can think on their feet [like] Cherry-Evans and Tommy [Trbojevic].
"Sometimes the coach needs to look at how he does things, and it will be something I will have to learn with our personnel.
"I'm not sure I'm using them properly. We've got some good, young talented players there and trying to get your best players on the field is what the coach has got to do but did I do it right? I'm not sure I did."
Brown added that powerful second rower Ben Murdoch-Masila, who was sorely missed, is likely to be back for Sunday's clash with the Eels, while experienced centre Euan Aitken will also be in contention.
