But they have left the door slightly ajar pending what the Pride Of Dubai gelding does in Saturday's Gr.3 Higgins Concrete Manawatu Classic (2000m) at Awapuni.
A bevy of consistent performances in quality three-year-old races this season has seen TAB bookmakers install Desert Lightning a $2.40 favourite for the weekend's set-weights feature.
"He's the best performed horse in the race and I'm very happy with him going into this," Peter Williams said.
"He's done fine since the Derby. We're happy. He wouldn't be going otherwise. He's worked well this week. He's as good as gold."
A winner of the Gr.2 Avondale Guineas (2100m) at Pukekohe last month, Desert Gold finished eighth in the Gr.1 New Zealand Derby (2400m) at Te Rapa earlier this month, a performance Williams was typically frank in assessing.
"No excuses, he just didn't get the distance," the trainer said.
"He'll run out a strong 2000m on Saturday so long as they go a decent clip. We just wouldn't want them to go too slow."
Vinnie Colgan will ride Desert Lightning again on Saturday, as he has done for all previous eight runs this preparation, including his second placing in the Gr.1 New Zealand 2000 Guineas (1600m) at Riccarton in November and the Karaka Million 3YO Classic (1600m) at Pukekohe in January.
Williams conceded that Desert Lightning's campaign, which has seen him run every month since last September, was coming to an end, which could preclude him from a start in next month's Gr.3 Frank Packer Plate (2000m) at Randwick.
"This will probably be his last race. We were going to think about Australia but that might be a bridge too far considering the campaign he's had this year," Williams said.
"He's never stopped eating; he's never stopped working well. His coat is still good. That race is at the end of the carnival when the races are a bit lighter. It's highly unlikely he'll go now but let's first see how he goes on Saturday."
Desert Lightning was a $150,000 purchase out of Little Avondale Stud's Book 1 draft at the New Zealand Bloodstock National Yearling Sales at Karaka in 2021.
"I just happened to be walking past him so I went and bought him. I didn't do any checks on him but he seemed like a nice horse and I liked him," Williams said
"He's been quite an uptight horse but he's improved a lot. He's not nervy, just uptight, but he's got a lot better, just through us working with him and keeping him relaxed.
"He'll be better again next year when he's a bit stronger. Everyone thinks he's big and strong but when you get up close to him, he's not that big and he's still not that strong yet."
Desert Lightning will be the Williams' only runner at Awapuni but the couple will produce Saint Alice, Helsinki and Verstappen "as runners' chances" at Avondale on Saturday.
Meanwhile, Williams was excited about last-start Royal Descent Stakes winner Cool Change's prospects for Saturday week's Gr.1 Fiber Fresh New Zealand Thoroughbred Breeders' Stakes (1600m) at Pukekohe.
"She's come through that last win really well. She's absolutely thrived."