A last-minute drop-goal conversion from Damien Cook handed reigning champions South Sydney a 14-13 victory in the opening game of the 2016 Downer NRL Auckland Nines against old rivals the Sydney Roosters.

A long Bryson Goodwin line break from almost the first play of the day set the tone before the sides went try-for try with Alex Johnston and Kirisome Auva'a scoring for Souths, while for the Roosters veteran Braith Anasta wound back the clock to step his way over for a four-pointer.

Roosters young gun Latrell Mitchell backed up fellow young gun Joseph Manu to score but the try of the game came when a perfectly weighted downfield kick from rookie Roosters half Tyler Cornish saw UK import Joe Burgess streak downfield to win the race to the ball.

A late try from Souths winger Michael Oldfield, whose clumsy grounding was awarded, narrowed the gap before Cook's conversion handed victory to Souths, 14-13.

Goodwin admitted he surprised even himself by splitting the Roosters defence open so early in the match.

"I just jumped across and found myself in some open space, I wish I could have scored but that's alright. The first hit-up of the game and I went straight through, it was a bit surprising," Goodwin said after the game.

"We are pretty pleased with that win, it's a good platform to build off."

Anasta said the Roosters' youngsters showed plenty of promise despite the defeat.

"Joey Burgess showed some speed there, made a couple of good breaks and scored a try as well," Anasta said.

"Latrell was great as well. I thought Joey Manu was great for us. We have some good exciting players and they did well."

There were some fears over a possible shoulder injury to Johnston, who spent the final minutes of the match on the sideline, but he was given the all clear by the Rabbitohs after full-time.

South Sydney Rabbitohs 14 (Johnston, Auva'a, Oldfield tries, Cook goal) def. Sydney Roosters 13 (Mitchell, Anasta, Burgess tries).