Cook scored a brilliant 40 metre try to seal a thrilling 30-20 victory in a ding-dong top-of-the-table clash.

Smith finished a tough night on the sidelines as he came from the field with what appeared to be an ankle injury with six minutes left on the clock, but he was able to return to congratulate the Souths players after full-time.

Most fans would have rightfully gone to bed wondering if they had just witnessed the NRL grand final preview after Souths leapfrogged the Storm to move back to the top of the ladder.

Cook was outstanding, as was skipper Sam Burgess, teen winger Campbell Graham, and Sam's younger brother George.

As Phil Gould said during the Channel Nine commentary: "They are a seriously good football team. There are probably a few [clubs] who think they can win it, but this side can win it.''

When told about those comments, coach Anthony Seibold smiled and said: "Gus is involved in Penrith as well, so we have to remember that.

"He might be trying to take some heat off them. He's probably learned that from Wayne [Bennett].

"We were really pleased with our performance, particularly the second half-half. We were down 16-6, but led by Sam, John Sutton and Cody [Walker], we were really consistent in the second half.

"Cooky was really good, and he's been good all year. It was good to see him jump out of dummy-half and put pressure on the markers. But the big boys did a good job and Cooky can't do his thing unless they get quick play-the-balls.''

The good news will continue for Souths with Greg Inglis to return from a broken thumb in a fortnight. On a sour note, though, Adam Doueihi was forced from the field with a knee injury. Seibold said Doueihi would undergo scans, but the early feedback was it was ''season-ending''.

Souths trailed 16-12 at the break, but they muscled up in defence and were forever camped down the Storm's end of the ground.

The moment that truly brought the Souths faithful to life was when Cook darted out of dummy half and beat Nelson Asofa-Solomona, Felise Kaufusi, Billy Slater and Josh Addo-Carr to score.

It was extra special given the two-metre giant Asofa-Solomona had fallen on Cook only minutes earlier and appeared to injure his ankle. Cook's ability to beat Slater for speed and then stop and jink past Addo-Carr could not be underestimated.

Cook was a star in his first Origin series, and will be $1.01 to take over Smith's Australian No.9 jersey now the future Immortal has retired from representative duty.

First-year head coach Seibold got one up on his former master Craig Bellamy. He will be the NRL coach of the year, regardless of what happens in the final month of the regular season.

Addo-Carr's speed made the difference on the scoreboard in the opening 40 minutes.

He scored a spectacular diving try and then accelerated out of dummy half to find space and send Curtis Scott on his way.

Souths had the better attacking opportunities but the Storm made sure they made the most of their limited chances as good sides do.

There were some laughs just before the break when Graham was wrongly awarded a try by the video referee, which brought the crowd to their feet in a mock celebration and had the players giggling.

Sam Burgess has been an inspiration for most of the season for Souths and lifted for the big occasion, amassing nearly 200m in attack and leading the way in the Rabbitohs' outstanding defensive display straight after half-time.

He wanted referee Ashley Klein to keep an eye on the Storm's ''wrestle'' early in the game, and made sure Souths dished out a bit of their own the remainder of the night.

The tide turned in the second half as Souths put some sting in their tackles.

One Melbourne set went just 15 metres before Asofa-Solomona was pinged for an incorrect play-the-ball on the fifth tackle.

Souths will face another acid test next Friday night in the local derby against premiership fancies the Sydney Roosters, followed the Broncos up north.

The Storm, who were chasing their ninth straight win, will host bitter rivals Cronulla at home.