The International Federation for Equestrian sports (FEI) said Ringwood Sky Boy, 13-year-old mount of New Zealand eventing travelling reserve Tim Price, was first to set hoof on Brazilian soil.
The cargo plane, an Emirates Boeing 777 carrying 34 eventing horses from London Stansted, touched down at Rio's Galeao airport shortly before midnight.
The animals were then transported on trucks for the final leg of the journey along a "bio-contained" route from airport to the venue at Deodoro.
The flight was the first of nine over the Olympic period bringing in horses that will compete in dressage, jumping and eventing.
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The flight from Stansted contained British-based horses whose riders will be competing for Britain, Ireland, Canada, Australia, New Zealand, Zimbabwe, Brazil, Japan, Italy and China.
Others will follow from Liege in Belgium and Miami.
Eventing -- which involves dressage, jumping and cross country -- opens the equestrian competition in Rio with the team and individual dressage section starting on Aug 6.
(Reporting by Alan Baldwin, editing by Toby Davis)
