Souths' finals campaign has been dealt a massive blow despite winning their first match at Brookvale Oval since 2004, with inspirational skipper Roy Asotasi ruled out for the remainder of the season.

The Kiwi enforcer will undergo right knee surgery after snapping his anterior cruciate ligament in the 65th minute when he was pulled down just short of the Manly tryline.

Club medical staff immediately ruled him out for the season and the end-of-year Quad Nations tour, souring Souths' impressive trouncing of the Sea Eagles in front of 15,702 fans at Brookvale Oval.

It is the second successive season Asotasi's season has been cut short - last year he ruptured his pectoral muscle in round 25 and missed New Zealand's victorious World Cup campaign.

''It's disappointing,'' he said. ''From the moment I got into that tackle I knew something was a bit different. I just felt my knee go outwards.

''I'm not having any luck in the last couple of years, I guess I'll have to start all over again.

''I'm really disappointed I can't be with the boys as they march for the finals. But we've got some depth in the club and we've got Scott Geddes, who I think is the perfect guy to take over my position.

''It's a team sport and I don't think one player will make a difference.''

Livewire hooker and Kiwi team-mate Issac Luke said the team was shattered at the news, but would be bonded by the absence of their captain and leader.

''There's a lot of leadership gone. And a lot of go-forward gone - he just showed what he could do against Manly. He won the game for us in the first half,'' Luke said. ''But we're gonna have these kind of hurdles, so we'll deal with it and we'll do it for Roy now.

''It leaves a big hole so it's gonna bring us even closer together. He kept us in the finals race last night, now we want to get there to pay him back.''

On the back of Asotasi's season-best performance, Nathan Merritt and Beau Champion each scored doubles as Souths moved within a point of an ill-disciplined Manly outfit on the NRL ladder.

Manly skipper Matt Orford blasted his side's discipline and commitment, with the Sea Eagles now just one loss away from dropping out of the eight after giving away nine penalties and completing just 69 per cent of their sets to Souths' 90 per cent.

''The disappointing thing was our error-rate was way too high and just the ill-discipline across the park. That sums it up,'' Orford said. ''Once again we found a way to mess up our game and put us in a vulnerable position. We've got a lot of work to do.''

Manly looked set for a big win when they shot to a 12-0 lead after as many minutes through tries to Tony Williams and Anthony Watmough.

But the Rabbitohs got back within six thanks to the magical boot of John Sutton, grubbering back inside for fullback Merritt to pounce under the posts.

It was the start of the thrilling comeback from the visitors, winger Fetuli Talanoa steam-rolling a confidence-shot David Williams to cross next on the far left. And by the 24th minute the Bunnies had taken the lead, giant debutant Chris McQueen crossing for his first NRL try.

And just six minutes later the 104kg debutant repaid the favour to Champion, who set up the earlier try, beating Tony Williams to the high ball and getting away a miracle off-load for Champion to stretch the lead to eight. Sandow's boot made it 22-12.

''Wolfman'' made two simple first-half mistakes and the brain explosions continued for Manly - Watmough penalised for going on with a tackle before launching a verbal assault on the touch judge.

Manly's attacking play inside the Rabbitohs' half was well below par in the second stanza.

Sandow scored the first points of the second half after a play-the-ball infringement gifted Souths a conversion in front of the posts.

With the lead out to 12, Manly finally struck back out wide through winger Tony Williams. But the match was put to bed at the 72nd when Merritt crossed for his second, before Champion followed suit in the 77th. Prop Jason King scored a consolation try for Manly in the final minute.

Coach Des Hasler was livid with his team's performance and just as critical of the 9-5 penalty count in Souths' favour, questioning the referees' decisions that saw Souths shoot out to an 8-3 lead in penalties.

SOUTH SYDNEY 36 (B Champion 2 N Merritt 2 C McQueen F Talanoa tries C Sandow 6 goals) bt MANLY 22 (T Williams 2 J King A Watmough tries M Orford 3 goals) at Brookvale Oval. Referee: Ben Cummins, Brett Suttor. Crowd: 15,702.