The five-year-old gelding stormed home in the final 300 metres of the weight-for-age 1,200-metre sprint to seal the A$6.2 million ($4.4 million) first prize in front of a raucous crowd that had been subject to COVID-19 restrictions.
Bivouac finished second, with Gytrash third.
The total prize pool was about A$15 million.
"It's all in the genes," trainer Les Bridge said. "Some horses just get all the good genes.
"This horse has just got a big V8 motor."
Eduardo led from the start and held on until the final 300 metres when McAvoy, who has now won three of the four The Everest races contested, piloted the big grey to the outside and stormed home by more than a length.
The Everest is not classed according to traditional horse racing conditions.
Investors buy one of the 12 slots available for A$600,000 and they can then nominate their own horse or approach other owners to enter a horse and then share the prize money.
The world's richest horse race is the US$20 million Saudi Cup, which is raced over 1,800 metres on a dirt track in Riyadh, with first place receiving US$10 million. ($1 = 1.4124 Australian dollars) (Reporting by Greg Stutchbury in Wellington; Editing by William Mallard)