Morris darted over for his second try of the night three minutes into golden point, sealing the Dragons' heart-stopping 22-18 win over table-topping South Sydney at ANZ Stadium on Monday night.

The Dragons trailed 18-6 with just 10 minutes remaining, but produced a rabbit-out-of-the-hat comeback to keep alive their faint finals hopes.

They'll have do it without Cooper though, with the intial diagnosis he had suffered a season-ending pectoral muscle tear.

The 34-year-old leapt high in an attempt to pluck a Nathan Fien bomb out of the air, but plunged into the turf after somersaulting over teammate Josh Dugan.

He took his place in the line for the next defensive set, but was quickly whisked off the field and up the tunnel shortly after. The off-contract Cooper will be sent for scans on Tuesday with his 14-year, 243-game career in grave doubt.

He had delayed a decision on his future until returning from a near three-month injury lay-off with a chronic toe problem.

"It's shattering for Matty," Dragons coach Steve Price said. "He's had a very tough year this year with his foot and it looks as though he's ruptured his pec.

"We'll get more scans [Tuesday] and make sure that's confirmed."

Dragons high performance director Andrew Gray added: "Unfortunately it appears he's ruptured his pectoral muscle. We'll scan him [Tuesday] to confirm that, but at this stage it doesn't look good."

Cooper's injury will take some of the gloss off a Dragons performance many thought not possible, with bookmakers ranking them at their biggest quote since they stunned a high-flying New Zealand across the Tasman in 2002.

But despite a litany of errors which have blighted their season, they constantly troubled the Greg Inglis-less Rabbitohs and trimmed South Sydney's cushion at the top of the ladder to just two points.

Morris sealed it when he scooted over from a Nathan Fien pass to decide the first golden point game by a try since the Roosters-Tigers qualifying final thriller in 2010.

Price lauded his side for "fighting like bulldogs" with the Dragons still needing to win six of their last seven matches to have any hope of featuring in the finals.

"It's important we build off that and get a bit of confidence and get into the Raiders at home next week," he said.

"I'm really proud of the guys as we're renowned as frontrunners, the Might And Power for a number of years now, and to come back when we were down at half-time against a really good footy team [was fantastic].

"We've got a playing group and a football club which believed in themselves [Monday night] against a very good football team and the competition leaders."

The result revived memories of the Rabbitohs' stunning 41-6 thumping of the then table-topping Dragons in 2009, which sparked and end-of-season fadeout from the Red V.

But a cautious Dragons skipper Ben Creagh refused to be drawn on whether it can inspire an unlikely Dragons finals charge.

"It's a long way to look back," Creagh said. "It was nice for the young guys and the boys who have struggled a little bit to put in a good performance."

Dylan Walker's converted try was the only thing separating the sides at the break, but the Rabbitohs appeared in control when Sam Burgess crashed over to pad their lead to 12 mid-way through the second stanza.

Morris and a fortuitous try to Adam Quinlan, playing his first NRL game at five-eighth, set up a field goal-a-thon in the final five minutes, but neither side could find the mark.

It was left to Josh Dugan, one of three Dragons players who had previously attempted to kick one-pointers, to provide the difference.

He ran the ball on the last three minutes into golden point when his planned field goal was rushed, grubbering into Ben Te'o and re-gathering to set up another set of six. Fien laid on Morris' match-winning try on the subsequent play.

ST GEORGE ILLAWARRA DRAGONS 22 (Brett Morris 2, Trent Merrin, Adam Quinlan tries; Chase Stanley 3 goals) defeated SOUTH SYDNEY RABBITOHS 18 (Dylan Walker, Adam Reynolds, Sam Burgess tries; Reynolds 3 goals) at ANZ Stadium. Referee: Gavin Badger, David Munro. Crowd: 14,571.