Wallabies captain Stephen Moore knows what it's like to face a formidable rival from across the Tasman and he has thrown his support behind the Diamonds as Australia's rugby and netball teams prepare to face arch-rivals New Zealand at Sydney Olympic Park this weekend.

Moore will on Thursday send a letter to Diamonds captain Laura Geitz, who tips the Wallabies to narrowly beat the All Blacks in their Rugby Championship decider at ANZ Stadium on Saturday night.

"I'm going for the Wallabies and I think they'll get up by three," Geitz said on Wednesday. "I know it's a massive ask, but I've just got a feeling."

Moore will send his letter "on behalf of the Wallabies" in the build-up to the netball team's World Cup clash with the Silver Ferns at Allphones Arena on Sunday.

"I think as a fellow national team, I just wanted to give them our support for their World Cup," Moore said on Wednesday. "It's here in Australia, which is good. We will be able to watch them. It's important for us to show our support there. I hope they do really well.

"They have obviously had a couple of fantastic years and they have a very big rivalry with New Zealand, as do we.

"I think there is a lot in common between the two sports."

What could the Wallabies glean from the Diamonds' success that may help the Wallabies?

"If there was one thing, some of the games I've seen of netball is that a lot of them go right down to the wire," Moore said.

"There is often just a point in it either way. Something you learn from watching that is making sure you play to that final whistle. That's been pretty evident in the games we've had against New Zealand in the last couple of years.

"They've certainly been tight, particularly last year. Every play counts right up until the final whistle."