Fireworks sparked early and continued through the match when Josh Reynolds was put on report for kicking Souths centre Campbell Graham in the head while striking out at a loose ball.

The pair were chasing through a kick from David Nofoaluma and as Campbell was falling on the ball, Reynolds threw his boot towards it, collecting a forehead instead.

With Campbell prone on the Bankwest Stadium turf, a scuffle ensued as Mitchell rag-dolled Reynolds, and he was lucky not to be sin-binned for the retaliation.

The Souths fullback collected Reynolds high around the back of the head with a swinging arm before throwing him to the ground, which is expected to draw sanction from the match review committee.

It went unpunished on the field, but he was put on report later for a careless high shot on Tigers forward Luke Garner in the 62nd minute.

Coach Wayne Bennett said he did not pay close enough attention to Mitchell's shot on Reynolds but is bracing to be without his fullback next week against Newcastle.

"I can't concern myself with that, it's happened," he said.

"The second one was certainly pretty head high but it wasn't a grade three or a grade four."

At the time the Rabbitohs led 18-0 thanks largely to a hat-trick from Gagai who ran riot on the right edge.

Uncharacteristically, Souths halfback Adam Reynolds missed all four conversions from the right touchline, kicking one penalty goal for the match.

And while the Tigers were tough and mounted a comeback with two late tries once Benji Marshall was unleashed in the final 30 minutes, they were essentially victims of their own first-half ill-discipline.

"We put a lot of pressure on ourselves and credit to Souths, they put a lot of pressure back on us," said Tigers coach Michael Maguire.

"We didn't take our opportunities in the second half, so I'm very disappointed."

Souths took advantage through Gagai twice in six minutes with the winger running in to score two quick tries on the right edge against Tigers debutant Reece Hoffman.

It was a mammoth task for the 19-year-old to mark the Queensland winger after being called in late to replace Tommy Talau who was withdrawn due to a hamstring injury.

James Roberts out-muscled him soon after half-time for his first try of the NRL season.

"They put us under some pressure there," Maguire said of the left-edge defence.

"At times there young Reece... I thought for his debut he actually played well.

"He obviously had some attacking raid going his side but I think there was a fair bit going on on in the inside that actually affected that as well."

Hoffman had a moment of joy in the 69th minute when he scored the Tigers' second try to raise the intensity of the final minutes.

As well as Mitchell, Souths forward Mark Nicholls could be in trouble after he was put on report midway through the second half for a crusher tackle on Josh Aloiai.

Australian Associated Press