Gelding initially passes-in before deal done to make him an Inglis record-breaker.
Kosgei will continue his career in Hong Kong after this week setting a new mark for the highest-priced male horse sold via an Inglis Digital sale.
The three-year-old son of The Autumn Sun realised a top bid of $750,000, which was initially under reserve, but a deal was later done that saw the last-start Victoria Derby fourth placegetter go to Daniel Yeung and Magus Equine.
Kosgei's price tag bettered the previous best for a colt/gelding by $150,000, previously held by Ranch Hand.
Magnus Equine's Willie Leung was thrilled a deal was able to be struck for the gelding who had just five starts for Trent Busuttin and Natalie Young and will now be joining Hong Kong trainer Michael Chang.
"I met with (Inglis Hong Kong Representatives) James Price and Alan Ho in Hong Kong in the days after the International Races and they advised me of the upcoming sale of Kosgei," Leung said.
"They provided me with a comprehensive prospectus document on the horse which was very helpful and informative for me and my client.
"Mr Yeung and his trainer Michael Chang have enjoyed good success together recently and Mr Yeung was keen to support Michael with a nice young horse.
"Kosgei is obviously a top-class racehorse with a lovely pedigree and being a son of The Autumn Sun, he looks to have a nice profile to develop into a Hong Kong Derby prospect as a four-year-old.
"He will travel to Hong Kong in the next shipment and be given some time to acclimatise before starting his race career there."
Kosgei was the headline act of a huge final Inglis Digital sale for 2023 with Chris Waller-trained Kitten's Joy mare Frumos selling to The Racing League for $245,000.
In My Feelings, a daughter of Manhattan Rain sold to Deere Bloodstock for $220,000 with a Stay Inside filly at foot, Siyouni mare Trust, who is in-foal to Kingman, was bought by Suman Hedge for $155,000, while unraced three-year-old Harry Angel filly Grinzinger Crown sold to Walnut Farm for $100,000.
The Inglis Digital December Online Sale grossed $5,261,700, making it the fourth Inglis Digital auction of the year to gross at least $5m.
The first Inglis Digital Sale of 2024 will be the Inglis Digital January Online Sale, which will run from January 19-24 with entries for that sale to close on January 17.
