Billy Slater and the Melbourne Storm are favourites for the NRL Premiership.
Billy Slater and the Melbourne Storm are favourites for the NRL Premiership. Hannah Peters

Will the purple reign yet again?

MELBOURNE has stormed into outright premiership favouritism for the first time this season following yet another narrow win which made it seven victories in a succession for the reigning champions.

The 12-6 victory propelled the Storm to the top of the NRL table for the first time this season, a move mirrored in Ladbrokes betting market after South Sydney's shock defeat to Wests Tigers.

Melbourne firmed from $5 into $4 with Ladbrokes, while the Roosters beatdown of Manly saw them wound in from $5 to $4.50, to now sit on the second line of betting ahead of the Rabbitohs.

One punter will be hoping the Roosters' hot form continues after wagering $25,000 on the chooks winning it all at $5.50 in May, while another is cheering Melbourne after they outlaid $8600 when the Storm hit a season high $8 on April 9.

The Bunnies eased from $4.50 to $5 after failing to register a 10th straight win.

"The fluctuations in the betting market has become as near an interesting sideshow as the jostling in that top group of teams," Ladbrokes spokesman Roger Oldridge said.

"One week you've (Souths) won 9 in a row and then after producing a flat one your probably due for, the bookies are easing you out."

St George Illawarra, who has spent a majority of the season as the premiership favourite, firmed in slightly after the weekend to be on the fourth line of betting at $7.50, having hit a four-month high of $8 after their round 18 loss.

The Wests Tigers face an uphill battle to make the top eight but that hasn't deterred a string of punters who backed them at $151 after their win over the Dragons last week and again at $101 following that victory over the Bunnies at the weekend. They are now $51 and continue to be backed.

Penrith hit its biggest price since round 11, easing from $7 to $9 after they were belted by the Broncos on Friday night. A result which saw Brisbane firm from $21 into $15.

The Sharks remained steady at $9 while the Warriors are now the longest price of any team in the top eight, out to $21.