Sydney 2000 Olympic gold medalist Stuart Tinney, and Beijing 2008 Olympic team silver medalists Megan Jones, Sonja Johnston and Shane Rose, are among the starters in CCI4* event.
Johnstone, 23, who is based in the Waikato, is a leading chance in the class of 11, riding the 12-year-old Orient Express. The "WEG special class" was put on as a last selection trial, and organisers waived the entry fees.
"As all the riders need to do this class as part of their final preparation for WEG and there is no prizemoney we felt it was the right thing to do," said event director Rose Read. "Even though our event budget is very tight we are very pleased to be able to help them on their way to Kentucky."
In Sydney's CCI3* class, Kiwi rider John Twomey starts Flaunt It and Highly Recommended. Other Kiwis in action in Sydney include Diane Gilder and Foreal in the CCI2* class, and in the CCI1* Blair Richardson rides Sailor Sam and Knightrider, and Laura Wallace rides Charlton Ultra and Sugoi, who was ridden at the 2008 Olympics by Heelan Tompkins.
Other Kiwi WEG contenders in action this weekend are British based riders Andrew Nicholson with Nereo, Mark Todd on Grass Valley, Joe Meyer on Clifton Lush and Jonathan Paget on Clifton Promise.
Meyer's top horse Snip fractured a bone in his hock just days before the Hartpury selection trials, putting him out of contention, and Paget had an unfortunate fall in the cross-country at Hartpury on the back of posting the highest Kiwi score in a friendly against the Australians earlier in the week.
Equestrian Sports New Zealand eventing chef d'equipe Erik Duvander faces a difficult selection, with some impressive and solid performances from all of the seven on the short-list - the other being Caroline Powell on Mac MacDonald.