The Green Machine's second-half woes continued as they went down 34-20 to South Sydney at Canberra Stadium on Thursday night.

It's the first time they've lost four in a row since 2018.

But the bunker left NRL Immortal Andrew Johns scratching his head after it ruled out a Jack Wighton try with three minutes remaining - ending the home side's chances.

The home crowd of 14,260 let the officials know exactly what they thought as they left the field - with the Raiders on the wrong end of an 8-1 penalty count.

Bunker official Henry Perenara ruled obstruction against Corey Harawira-Naera, despite the Canberra second-rower making no contact with the Souths defensive line.

"The decoy runner didn't cause any dramas for the defence," Johns said in Channel Nine commentary.

Wighton had another try disallowed just minutes earlier when Emre Guler was ruled to obstruct Benji Marshall.

Raiders winger Bailey Simonsson was put on report for a lifting tackle on Cody Walker, although he shouldn't have too many concerns.

The Rabbitohs lost lock Cam Murray to an ankle injury he suffered early in the first half, while Raiders centre Sebastian Kris also injured his ankle - although he was able to finish the game.

For such an important game, it couldn't have gotten off to a worse start for the Raiders.

Trying to break a three-game losing streak they lost England halfback George Williams (hamstring) in the warm-up forcing Canberra coach Ricky Stuart into a massive pre-game shuffle.

Second-rower Elliott Whitehead, already filling in as acting captain, shifted to five-eighth with Hudson Young coming into his back-row spot and Sia Soliola coming onto the bench.

Despite all the early adversity and after Reynolds converted an early penalty, the Raiders scored the first four-pointer.

A nice Caleb Aekins cut-out pass parted the seas for Jordan Rapana to score in the corner.

Rapana assumed the kicking duties with Jarrod Croker (shoulder) and Williams both out.

Marshall's been enjoying a late-career renaissance and he unleashed a wicked cut-out pass of his own for Alex Johnston to score in the corner.

Whitehead, playing as a big, ball-running five-eighth, fended his way through the Souths defensive line to crash over with Rapana's kick putting the home side in front.

Rapana extended their lead after Kris got on the end of a Wighton grubber in behind that Souths winger Jaxson Paulo made a meal of.

A questionable call from the bunker saw the Rabbitohs hit back - Kris was ruled to have touched a ball that went into touch, although the Raiders centre didn't appear to play at it.

His opposite number, Campbell Graham, sliced through the Canberra line to make it just a two-point game at half-time.

Could the Green Machine turn around their second-half woes?

They went into the clash having only scored four points in the past three second 40s.

It didn't get off to a promising start when Dane Gagai finished off a massive overlap just five minutes into the final stanza.

Souths went back to their left-edge attacking well again as a nice Reynolds kick-dummy froze the Raiders line and then they proceeded to run Johnston in for his second.

The emerging dominance down that side of the field forced Stuart to swap Rapana to the right wing and Simonsson to the left.

But then second-rowers then combined with Jaydn Su'A getting on the outside of a Keaon Koloamatangi linebreak.

Rapana's switch to the right edge led to his second try of the night.

A brilliant Curtis Scott show-and-go saw him slice through before putting the New Zealand international away to keep the game alive.

It also ended 126 second-half minutes without a point for the Green Machine in the process.

But that was the end of the comeback despite the Raiders continuing to press to the end.

"The second half has become our Achilles heel," Rapana said.

AT A GLANCE

SOUTH SYDNEY RABBITOHS 34 (Alex Johnston 2, Campbell Graham, Dane Gagai, Jaydn Su'A tries; Adam Reynolds 7 goals) bt CANBERRA RAIDERS 20 (Jordan Rapana 2, Elliott Whitehead, Sebastian Kris tries; Rapana 2 goals) at Canberra Stadium. Referee: Ben Cummins. Crowd: 14,260.