The Rabbitohs had taken care of the Roosters, Dragons and Titans in the first three rounds but Wayne Bennett sensed his side would break under pressure after observing a softening of attitude at training.
The Rabbitohs only lost to the Sea Eagles by one point (13-12) but Bennett wasn't happy with what his side displayed out on the park at Lottoland on Saturday afternoon.
"I just thought we got what we deserved," Bennett said.
"We were average. It was the attitude today that killed them.
Match Highlights: Sea Eagles v Rabbitohs
"We've been heading in that direction - our performances have been getting worse since we played game one. We haven't played a game for 80 minutes yet.
"Hopefully it reminded them all that they've got the prepare better."
Halfback Adam Reynolds was far from his best, uncharacteristically missing three goals and two field goals - most of which were in kickable range.
Although their No.7 wasn't able to seal the deal as he has done so many other times in clutch situations, Bennett said the result was a reflection of the entire team's performance.
"It's never one guy when we play that way - it was the whole lot of them out there," Bennett said.
"Adam wasn't by himself, believe me.
"I know how hard he practises with it, it was just one of those days."
The Bunnies don't look like they will be able to count on Greg Inglis returning in round five to lift the side with Bennett unsure of when his skipper will get back from a shoulder injury.
"He's got more movement in his shoulder but I don't know if it will be next week or the week after - it's going pretty slow at the moment," he said.
Walker and Reynolds create space for Burgess