Murray Baker won't compare his other Australian Derby winners to current hope Jon Snow, but a consistent thread is emerging as New Zealand mounts a two-pronged assault on a focal point of The Championships' opening day program.

The three-year-old has made significant strides towards Randwick and the Group One staying feature over 2400m on Saturday by tackling the same distance back home in the New Zealand Derby at Ellerslie on March 4.

Gingernuts, the Australian Derby favourite with the TAB, and Rising Red beat Jon Snow to the line that day but for veteran trainer Baker, the New Zealand Derby is tailor made for a successful Randwick raid.

Tavago employed the same strategy before winning the Australian Derby 12 months ago.

Mongolian Khan, the most recent of Baker's three Australian Derby success stories, achieved the Derby double in 2015 though the prolific It's a Dundeel (2013) spent his build-up in Australia and Nom Du Jeu (2008) snuck up on the locals a month after winning at Group Three level at Awapuni.

James Cummings, trainer of Victoria Derby winner Prized Icon, concedes the New Zealand horses have arrived battle hardened and Baker agrees, describing the NZ Derby as the ideal launch pad.

"It gives you an idea of whether they can stay, and it's become a very tough race in New Zealand since it was shifted from Boxing Day to the start of March (in 2006)," Baker said.

"It means there's more competition. The horses are another couple of months older and a bit stronger."

The benefits of a tough lead-up race was apparent when Gingernuts skipped over the heavy ground to snare the Rosehill Guineas.

Jon Snow then thrived in identical track conditions in the Tulloch Stakes last weekend.

"Obviously it's a lot stronger race this week but we think he's strengthened up, and he doesn't mind wet conditions" Baker said.

Randwick was rated soft early on Thursday but with a return of the rain it was downgraded it was in the heavy range by the afternoon.

It was pointless to draw a comparison, Baker said, between Jon Snow and his Australian Derby predecessors but the $7.50 third favourite was maturing nicely.

"It's hard, they're racing on different tracks but I think this guy's a good stayer," he said.

Other than Gingernuts, who won the NZ Derby by 2-1/4 lengths, Baker nominated second favourite Inference as a major threat.

Co-trainer Michael Hawkes was upbeat about the Randwick Guineas winner after Inference's last-start second to Gingernuts in the Rosehill Guineas on March 18.

"It's an ideal distance for him," he said.

"The two Kiwis, they're in with a good chance. They're both great last-start winners but our bloke is on the rise and it's certainly a race he's going to be competitive in."