With the match evenly poised in the first half on Thursday, Penrith fullback Dylan Edwards cut through the Rabbitohs' line on a scrum play to open up an eight-point lead for the Panthers.

In the lead-up, Panthers centre Izack Tago ran a decoy line in between Lachlan Ilias and Campbell Graham and contacted Ilias's outside shoulder, which usually constitutes an obstruction.

But the Bunker ruled that given Edwards was able to outrun Graham, who was closer to him, Ilias would still not have reached the ball-carrier had he been left untouched.

"I don't think there's anything else that Izack Tago can do (to get out of the way of the defenders)," Michael Ennis said in commentary for Fox League.

"I think they got it right."

In a similar incident last week, Newcastle's Bradman Best was paid a try against Brisbane despite a decoy runner contacting Adam Reynolds on his outside shoulder.

Quizzed about the decision to award the try at his weekly briefing on Monday, the NRL's head of football Graham Annesley said the match officials were permitted to use discretion in applying the obstruction rule.

"The referee or review officials can determine the significance of contact initiated by the 'Block' or 'Flat' runner(s) in impeding a defender's involvement in a try scoring play," the NRL's rules read.

Demetriou said he was still confused by the rule.

"Honestly, I've given up trying to figure out what that rule is," he told reporters.

"(Tago) stops in the line. There's no way Lachie can get off that."

While the Panthers went on to win by only four points, Demetriou refused to blame Edwards' try for the loss, which looks to have ended South Sydney's last-minute top-four bid.

Instead, he lamented his side's inability to stifle the Panthers' attack despite the absence of creative architects Nathan Cleary (suspension) and Jarome Luai (MCL injury).

"We shouldn't have conceded 26 points in a game when they're missing their two most creative players," he said.

"We needed to get in front on the scoreboard and put some pressure on them to make a play and we weren't able to do that up until the last few minutes.

"A few blokes missed their assignments in defence tonight and that's what cost us."

Australian Associated Press