Ireland's Judy Reynolds and her horse Vancouver K finished 18th in the final of the Equestrian individual dressage.
Team GB's Charlotte Dujardin retained her title with a record score of 93.857 aboard Valegro.
Reynolds' score of 75.696 was enough for 18th and bottom place among the finalists.
"I'm absolutely delighted with how Vancouver K has performed all week and he again gave his all in the arena today. I'm very proud of what we have achieved on our Olympic debut," she said.
Germany won the silver and bronze with Isabell Werth (89.071) and Kristina Broring-Sprehe (87.142) rounding out the podium places.
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