LONDON — The poised 15-year-old stepped into the arena Thursday as the crowd fell into a polite hush. For six minutes she pranced and pirouetted, and when it was all over, her team pronounced the performance a smashing Olympic debut.

The teenager in question? Rafalca, the most famous American athlete on more than two legs at these Olympics. But her renown is due only partly to her prowess in the esoteric sport of dressage, best described for the uninitiated as an intricate form of equine dancing.

In the stands at London's Greenwich Park was Rafalca's co-owner Ann Romney, wife of Republican presidential candidate Mitt Romney, whose connection to the rarefied world of big-time equestrianism has prompted interest in the sport unlike anything American riders have seen before.

Ann Romney "was absolutely ecstatic" after Rafalca, a German-bred mare, placed 13th among 25 horses that appeared Thursday, said Kenneth Braddick, a family acquaintance who edits the website Dressage-news.com and attended the competition. Three more U.S. horses are set to go Friday, with the top seven national teams advancing to the final round Tuesday.

In an election campaign that's focused on the economic woes of average Americans, the regal Rafalca, with her rich brown coat and white socks, has unwittingly provided plenty of fodder for Mitt Romney's Democratic critics. Dressage looks, and sounds, like a sport for the 1 percent.

In dressage, horses are expected to perform a series of delicate maneuvers set to music — trots, skips, turns and jaunty sashays — at the subtle direction of riders who wear top hats, white gloves and jackets with tails and brass buttons. The moves go by names such as "piaffes," "passages" and "flying changes," and at the sport's highest form "the horse should look like he's having a good time," said Anne Buvik, the editor of Hestesport, a Norwegian horse publication.

World-class competition horses are valued in the millions of dollars, and the cost of housing and caring for them can run to more than $50,000 annually. (The Romneys reportedly spent $77,000 a year for Rafalca's upkeep.)

Insiders say the sport is no more elitist than any other Olympic-level pursuit. Rafalca's rider, Jan Ebeling, learned to ride while growing up in Germany. Another rider, Michal Rapcewicz, noted that in his native Poland, a riding lesson is roughly the price of a movie ticket.

"Rafalca was not an inordinately expensive horse," said Braddick, of Dressage-news.com. "When you look at young ice skaters whose families move to Colorado Springs or Usain Bolt, being massaged and chiropracted and all the rest of the stuff that happens to him every day ... it's all pretty heavy going at that level."

After Rafalca and Ebeling completed their routine Thursday, the crowd — packed into the arena to cheer on a favored British team — applauded warmly. (Spectators are advised not to clap too loudly at the start, lest it spook the horse.) There was no sign of ill will stemming from Mitt Romney's pre-Olympic comments questioning whether London was prepared to host the Games.

"There certainly was a lot of media attention going on, but I think it really ended up being a good thing for the sport," said Ebeling, of Moorpark, Calif. "And I don't really get distracted by these things. I have a pretty good way of focusing."

Ebeling, 53, didn't speak to Ann Romney before the competition, but afterward she expressed her pleasure: "That was awesome."

Ebeling, in riding boots, white pants and a dapper navy jacket with tails, also seemed thrilled with the performance, smiling wide and waving to the crowd.

"She was great," he said about Rafalca.

Mitt Romney's Democratic critics also found the performance great, for a different reason. Hours after Rafalca's performance, the liberal group MoveOn.org said it would run 30-second ads in key states mocking the Romneys' expensive hobby, featuring an English-accented Rafalca saying: "After Mitt Romney repeals health care and ships your jobs overseas, I daresay your life won't be nearly as pampered as mine. After all, you're not one of his horses."

Material from The New York Times is included in this report.