Markus Schreiber, Associated Press
Great Britain's Zara Phillips runs with her horse High Kingdom during horse inspection for the equestrian eventing competition at Greenwich Park, the site for the equestrian and modern pentathlon events at the 2012 Summer Olympics, Friday, July 27, 2012, in London.
The crowd was unbelievable! —Zara Phillips

LONDON — Zara Phillips, Queen Elizabeth II's granddaughter, raced through the difficult and dangerous cross-country portion of her first Olympic equestrian eventing competition Monday, finishing clean and well under the pace time as she was cheered on wildly by thousands of fans, royal and not.

"The crowd was unbelievable!" Phillips said after she finished. "I hope I didn't take any heads off on the way cutting corners."

Princes William and Harry watched her from the main equestrian arena, joined by William's wife, Kate, and Camilla, the wife of Prince Charles. Seated alongside them were Princess Beatrice and Princess Eugenie, the daughters of Prince Andrew.

Phillips' mother, Princess Anne, watched from the grounds of the twisty, hilly 5.7-kilometer (3.5-mile) course dotted with 28 obstacles.

Phillips said her time of 9 minutes, 55.11 seconds — well off the 10-minute, 3-second time limit — was particularly good given that her horse, High Kingdom, lost a shoe during the ride.

"He did amazing," she said. "He really grew up and stepped up to the plate." She said the only drawback to the raucous cheers from the crowd was that she couldn't hear the timer on her wrist ticking.

The thrilling cross country portion of the three-discipline eventing competition is designed to test horse and rider endurance — and guts — and the course up and down the hills of Greenwich Park fit the bill. There were razor-sharp turns, blind 2-meter (yard) drops and tricky combination jumps — each one designed with a very British story behind it.

The first few horses out Monday seemed to handle the course relatively well, but as the afternoon wore on more than a half-dozen riders fell from their mounts and several horses slipped on the tight turns.

"He was slipping in the warmup so I changed to longer studs for the course," said American Karen O'Connor of Mr. Medicott, a horse purchased for her from the gold medal-winning German team four years ago. O'Connor earned 5.6 penalties for exceeding the time limit and was in a provisional eighth place about halfway through the competition.

Germany's Ingrid Klimke, part of the gold-winning German eventing team in 2008, was in provisional first place riding Butts Abraxxas.

Several of the riders who fell wore protective vests that inflated much like airbags upon impact.

Thousands of people lined the narrow course to watch the horses, getting an unusually close view of them and enjoying a festive picnic atmosphere on the grass.

The royals were watching the competition on big screens inside the main arena; the course comes into the arena itself for the 16th obstacle, a combination jump that's a miniature version of the Tower of London.

On Sunday, Phillips' grandfather, the Duke of Edinburgh, joined her mother in the VIP stands to watch her earn a respectable score in the dressage portion of her Olympic debut. With 46.10 penalty points for a slight mistake, Phillips landed in 24th place out of 74 riders. After cross-country, she'll compete in show jumping Tuesday, the final portion of eventing.

The course included English rose gardens to jump over, a tricky No. 3 combination jump that saw several refusals Monday, and even a swampy scene from the British children's classic "The Wind in the Willows." One tough jump depicts the Prime Meridian Line that runs nearby; another is a crescent moon, a nod to the Royal Observatory on the park grounds.

The course starts with a diamond-framed hedge in honor of Queen Elizabeth II's recently celebrated Diamond Jubilee. It ends with a giant, upside down horseshoe flanked by two equine sculptures made entirely of recycled horseshoes.

Phillips, a former world and European eventing champion who is 14th in line to the British throne, said she was thrilled to be representing Britain on her home soil — literally. Greenwich Park is the oldest royal park in London. The main equestrian arena sits in front of Queen's House, a 17th-century building designed as a summer palace for Queen Anne of Denmark, the wife of James I.

Her mother, Anne, competed at the 1976 Montreal Olympics, but her horse fell going over a jump during the cross country event. Phillips' father, Capt. Mark Phillips, fared better, winning team gold at Munich in 1972 and silver in Seoul 16 years later.

After the dressage portion Sunday, Germany was in the lead with 119.0 penalty points followed by Australia with 122.1 and Britain with 127.

Margaret Freeman contributed to this report.

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