NRL Round 18 Betting Preview: Game Odds, Trends, Analysis for Week Ahead

The Sydney Roosters and Melbourne Storm may be at the top of NRL Premiership markets, but the impact of State of Origin III means both go into their Round 18 matches as underdogs, according to AustralianGambling.com.au.

The Roosters host South Sydney on Friday night at Allianz Stadium having dealt with the same opposition 10-6 when they last met in Round 4.

But the oddsmakers have the Rabbitohs, who are 11th in the table, as $1.60 AUD betting favourites with the Roosters $2.37 with a four-point head start.

The reason is straightforward as the Roosters are without Mitchell Pearce, Boyd Cordner, Blake Ferguson and Dylan Napa, all of whom are on Origin duty. Souths don't have a single player on duty and have an excellent opportunity to get a big scalp here.

It's a similar story for eighth-placed Parramatta, who travel to Melbourne to face the Storm with pretty much a full-strength outfit. The Eels, who have won just one of four matches at AAMI Park, and just one of their past five against the Storm, are $1.58 to win this one.

Punters are avoiding the Storm given they have their best six players in the Queensland squad and they are out to $2.40 with a 4.5-point line in their favour.

A win in this one would be massive for the Eels, who can pull clear of the fight for the final spots in the eight and notch their fourth win in their past five matches.

Manly Sea Eagles are one of the form teams in the competition having won five matches in a row to surge to third but are only $1.91 equal favourites against Penrith, who have dropped their past two.

The absence of Jake Trbojevic, who is with NSW, is a factor in this market, whereas the Panthers, who are in ninth, go into this one virtually at full strength.

The Panthers have won just two of five matches at Pepper Stadium this season, but this is their first match at the ground in two months. The Sea Eagles haven't won there in six years.

In the weekend's final match, and the only Sunday fixture, Canterbury are $1.42 favourites against bottom-of-the-table Newcastle Knights ($2.90) at Belmore.

The Dogs may be languishing in 13th, but the Knights look unlikely to win another game this season having been thrashed by fellow cellar-dwellers Wests Tigers 33-12 last week.

The Knights haven't played at Belmore since 1996 and haven't won there since 1992.