Manly have begun life under Anthony Seibold with an entertaining 30-28 NRL trial win over South Sydney.

The Sea Eagles kept their hopes of claiming the inaugural NRL Preseason Challenge title - and the $100,000 prize that goes with it - as they collected 14 points from a possible 15 with the end-to-end win.

Neither side was at full strength, with most of their big names watching from the stands at Gosford's Industree Group Stadium.

There were a couple who pressed their case to Seibold and his South Sydney counterpart Jason Demetriou.

Young Manly winger Raymond Vaega grabbed a tryscoring double inside half-an-hour, while fullback Jake Toby set up three tries and bagged two of his own.

Cooper Johns laid on two try assists and kicked three goals in his first Manly outing.

"I'm enjoying having a lot of responsibility playing with a younger team," said Johns, who is expected to be Daly Cherry-Evans' understudy this year.

"There's a lot of talent and there's a real focus on being connected and our group is coming together really well."

For Souths, Blake Taaffe showed his class as he scored a try and set up another while playing at five-eighth.

Taaffe is expected to assume the bench utility role vacated by Kodi Nikorima after his move to the Dolphins.

The 23-year-old scored the try of the night when he put up a high ball, gave chase, and waited for winger Richie Kennar to bat the ball back into his arms and touch down.

Dion Teaupa crossed twice for the Bunnies in the first half while dynamic forward Zac Fulton barged his way over the line for Manly.

With the scores tied at 24-24, Manly got the upper hand when centre Leon Te Hau was sinbinned for a dangerous throw on Fletcher Myers.

On the ensuing set the Sea Eagles made them pay with Cameron Brown darting over in the corner and Johns converting.

Jarrett Subloo hit back for the Rabbitohs while they were down to 12 men but the former Canberra playmaker was unable to slot the conversion, allowing Manly to walk away with the win.

"I was very happy with Blake tonight," Demetriou said.

"There were some areas that let us down tonight, so we'll get some lessons from that and obviously fatigue plays a part with it being your first hit-out.

"We've got a lot of work to do defensively, but we're happy where we are at."