Led by a five-star kicking performance from Joe Williams, Wellington scored five tries to three to set up a shot at Parkes in this weekend's preliminary final.

The battle between two of the Group's most exciting teams turned into a grind due to the wet conditions that prevailed, and it was the Cowboys that responded better despite letting in the first try of the match.

Buddy Louie's four-pointer, which was converted by Corey Cox, gave the Rabbitohs a 6-0 lead but by half-time it was Wellington who were in front 18-6 courtesy of tries to Kotoni Staggs, Steve Riley and Williams.

Twice in the second stanza Westside got within six of their rivals through a pair of tries to Viliame Turuva, but it was Richard Peckham's late four-pointer which ultimately handed Wellington a 10-point win.

The prize for the Cowboys is a battle with Parkes this Sunday, with the winner to meet Dubbo CYMS in the grand final on September 6.

"I thought Westside were good but we were able to play field position and hold on to the ball," Williams said.

"The conditions didn't really suit either side but I thought given the weather it was a pretty good game of footy.

"The pleasing thing was that last week against Parkes we didn't play well but we took some things out of that game and improved on them today.

"We played a style of football that hasn't been traditional Wellington football and really grinded the game out.

"If we can do that again next week I'd like to think we're a chance of beating Parkes, but any team with Dennis Moran in it has to be respected because he is a hell of a player and he'll have them ready."

o WELLINGTON COWBOYS 28 (Kotoni Staggs, Steve Riley, Joe Williams, Lewis Stanley, Richard Peckham tries; Williams 4 goals) def DUBBO WESTSIDE 18 (Viliame Turuva 2, Buddy Louie tries; Corey Cox 3 goals)