But it was all for a good cause — to benefit 400,000 children of an AIDS-ravaged African nation.
But he had a smile on his face as he got up and continued the contest, which Figueras' Black Watch team won 6-5 in overtime. At first, the prince's Black Rock foursome was ahead, with Harry scoring an early 2 points, despite his fall.
"I think his horse got spooked, or something," Figueras told The Associated Press, adding, "It was a very tight match — right till the end, we didn't know who was going to win so it was very exciting to play."
But polo was not the main point of the day.
The United States "has always protected the downtrodden, the poorest, those most in need of help in the world," Harry said before the match. "And to me, this is what the United States stands for."
Harry played as part of his pledge to continue his mother's work. Princess Diana, who was often photographed embracing HIV-positive mothers and children, died in 1997 in a Paris car crash.
Sunday's heat, topping 90 degrees, "is a welcome relief after the snow and ice of Lesotho, where I was last week," her son said of the southern African nation where he said he took his brother, Prince William, to show him the work of his charity.
Earlier, Harry joined guests in the VIP "marquee" — a fancy white tent where lunch tables for 10 overlooking the field went for as much as $50,000.
While the day was meant to be a relaxing summer celebration, the combination of polo and royalty gave the occasion a decidedly formal air. Guests invited to be in the presence of "His Royal Highness Prince Henry of Wales" were also instructed on attire.
"Gentlemen" ought to wear a "summer suit," the invitations said, and the "ladies" were challenged to sport "their most daring hat." True to English tradition, many women showed up in what could only be called "daring" items atop their heads, from feathers to fruit.
Anyone bringing a child had to make sure each had "their own caregiver." No youngster was allowed in the VIP tent and was instead relegated to an adjacent area filled with games and snacks.
Proceeds from the day would go to American Friends of Sentebale, a charity set up in 2006 by Harry and Prince Seeiso of Lesotho for "the vulnerable children of Lesotho," where many children are AIDS orphans.
Harry said both he and the African prince wanted to follow the examples set by their mothers.
"Both were very much loved, and both loved people — both loved helping people who needed it the most," he said.
About 100 children in Lesotho lose one or both of their parents each day, Harry said, adding that the orphaned children survive with no prospects of a regular nourishing diet and little hope of a meaningful education.
Celebrity sightings at the Veuve Clicquot included Susan Sarandon, Julianna Margulies, Val Kilmer and Mary J. Blige. The tally for the day was not immediately available, but was likely hefty, given the minimum price for a table for 10 in the VIP marquee — $20,000. The $50,000 tables were closest to that of the prince. That included the champagne accompanying a meal prepared by chef Michael Romano of Manhattan's Union Square Cafe.
A picnic on the grass went for $250 per person.
Figueras told the AP that he plans to visit Lesotho sometime in the fall.
And though "I push him as hard as I can inside the polo field, we're all equal," the Argentine star told the AP. "Today, we all won because today was about those kids in Africa."
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