Rabbitohs coach Anthony Seibold has revealed Robert Jennings showed up to pre-season training overweight - but has since responded well to emerge as the NRL's leading try-scorer through 18 rounds.

Jennings bagged his third career hat-trick on Saturday against Canterbury to move to 16, one ahead of Warriors winger David Fusitu'a, but afterwards Seibold revealed the former Panthers flyer started the season off on shaky ground.

"He's been a real big improver for us this year," he said.

"Even his carries out of the back field for us really creates momentum. I've loved the way he's applied himself this year. 

"He turned up at pre-season training about eight kilos overweight so I kicked him up the backside to start with. Since then he's had to apply himself.

"He's been a lot more consistent with the way he trains and more consistent with his preparation."

Seibold laughed that Jennings is "probably never going to die of stress".

Match Highlights: Bulldogs v Rabbitohs – Round 18, 2018

"He's a pretty relaxed sort of guy. He's worked hard and he's had to because I wasn't happy with the way he turned up for pre-season on day one.

"He was coming from a long way back but something clicked for him at the back end of pre-season and he's carried that form and been more consistent so it's a credit to him."

Overall Seibold felt the team had been scratchy to start both halves in their eventual 24-6 win but was particularly pleased with the effort of the three Origin reps backing up three days after Holden State of Origin III on Wednesday.

"I was really proud of all there of the boys backing up, in particular Cooky (hooker Damien Cook), I thought he was outstanding. Really pleased with the way he applied himself," Seibold said.

Of the decision to give Cook an early shower eight minutes from fulltime, he added: "I thought it was the right thing to do to get [utility] Adam Doueihi some time so I took off Angus [Crichton], took off Cooky.

"Gags (Dane Gagai) has been through it all before. It was all about getting Adam some time."