"We would have lost that game last year, 100 per cent," Klemmer said after a victory that ensures Newcastle are well on their way to a first finals appearance since 2013.

"Our mentality, and what we went through in the off-season, training-wise we've been put in those situations. To get through that, it's big for the confidence."

Twice the Knights had to come from behind against Manly to earn a win that lifted them five points clear of ninth position, with six rounds left in the season.

Newcastle remain sixth on the ladder but are now only one point adrift of fourth-placed Sydney Roosters.

O'Brien said his team would "enjoy the win" but were focusing no further than Sunday's clash with North Queensland Cowboys - who upset the Knights 32-20 in Townsville less than two months ago.

"We're not looking at the top four ... I just don't think we can get too far ahead of ourselves," O'Brien said.

The coach added that "you can get caught if you start looking too far down the track".

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O'Brien said he was "rapt" with some parts of Newcastle's performance against Manly, in particular their determination to fight back from deficits of 12-0 and 24-20.

But he admitted it "was a bit of a roller-coaster" and a relief to emerge with a victory.

While the Knights shored up their position, the defeat left Manly four points outside the top eight, and stand-in fullback Brendan Elliot (knee) joined their casualty list.

"Equation wise I think there are still enough points," Manly coach Des Hasler said of his team's finals prospects.

"But in the past two weeks we have let four points go. We are making it very difficult.

"We are walking the tightrope now and we need to walk it well."

Hasler was disappointed that referee Ashley Klein penalised Manly 11 times, compared to the four that Newcastle conceded.

"That would be my only gripe. It kind of kept them in the game," he said.

Centre Enari Tuala was outstanding for Newcastle, scoring two tries, including the match-winner, while keeping Manly giant Moses Suli in check.

"You look at Enari Tuala, that kid just keeps making plays, whether it's with the ball or without," O'Brien said.

Manly raced to a 12-0 lead but the Knights recovered to hold a 16-12 advantage by half-time.

Newcastle opened their account in the 21st minute when winger Starford Toa scored in the corner from a Kalyn Ponga cut-out pass, then eight minutes later hooker Kurt Mann burrowed over from dummy-half.

The Knights edged ahead a minute before half-time when Toa batted down a Blake Green high ball, Lachlan Fitzgibbon offloaded and Tuala dived over.

The home side extended their lead six minutes after the break when a bomb from Mitchell Pearce ended up in the hands of winger Hymel Hunt, who scored in the corner.

Manly hit back to grab the lead after tries in the 53rd and 56th minutes, but Tuala's second try and an ice-cool conversion from Ponga sealed a vital win.