Equestrian: Zara Phillips stars as Team GB strengthen gold medal bid with superb cross-country performances

Zara Phillips delivered a stunning performance in front of 50,000 people on her Olympics cross-country debut at Greenwich Park today to keep Great Britain firmly in medal contention.

The Queen's granddaughter was watched from the main arena stands by the Duke and Duchess of Cambridge, Prince Harry and the Duchess of Cornwall - and she did not disappoint her audience.

The 31-year-old former world champion produced a clear round inside the time, completing a course that claimed its fair share of casualties.

Seven of the first 27 combinations fell and were eliminated, but Phillips kept supreme control all the way around a testing track that was very slippery in places.

Her team-mate Nicola Wilson also went clear inside the time aboard Opposition Buzz, while 51-year-old Mary King collected just 1.2 time penalties on Imperial Cavalier.

The British could not have hoped for better displays from their first three riders - and they still had former European champion Tina Cook and current world number one William Fox-Pitt to go.

Speaking after competing, Phillips said: "I am so happy. He is such a dude.

"He lost a front shoe, so he really stepped up. He was awesome - the course was very suitable for him."

Five combinations were clear inside the time as the competition entered its second half - Phillips, Wilson, Germany's Ingrid Klimke, Sweden's Sara Algotsson Ostholt and Australian Christopher Burton.

Phillips punched the air as she went through the finish to an ecstatic reception from an adoring crowd as she finished on her dressage score of 46.10.

Earlier, Canadian rider Hawley Bennett-Awad required medical attention after falling at fence three, with her condition described by organisers as "stable" while she underwent further assessment in an on-course ambulance.

Belgian Carl Bouckaert fell at the same fence, while Japan's Takayuki Yumira also parted company with his horse Latina, which required the horse being treated.

The combined effect meant that King and Imperial Cavalier were about 25 minutes late starting their round after Wilson had given the host nation a flying start.

The combination are regarded among the world's leading cross-country exponents, and they lived up to that billing.

The world and European team gold medallists delivered a brilliant round, finishing almost 12 seconds inside the time allowed of 10 minutes, three seconds.

An elated Wilson, who was called into the Olympic team after Piggy French's horse DHI Topper W suffered an injury last month, remained on her dressage score of 51.70 penalties.

Fans ran over to congratulate her after she finished finishing the course, some waving union flags. She pumped her hand in the air and waved.

"He was just unreal, what a fantastic horse," Wilson said.

"This is his favourite stage by far. When he gets to go cross-country day it's like all his birthdays and Christmases have come at once.

"He never fails to give me the wow factor."

King, meanwhile, utilised all her experience, kept concentration, and she completed the course with just 1.2 time penalties, taking her overall score to 42.10 and into the lead ahead of Burton despite being briefly held on course while Yumira's horse was attended to.

King danced with happiness when she looked up at the scoreboard and saw she was in the lead.

She ran over to kiss her daughter before speaking to journalists.

"It was a great place to be stopped, so it was an advantage to us really," King said.

"You can pick up the speed before they stop the stop watch that they've had running through your stoppage time.

"There was a nice straightforward fence ahead and I managed to gallop through it at a really nice stride"

Britain's dream day continued thanks to the efforts of Tina Cook and her double Olympic bronze medal winner Miners Frolic.

Cook matched the efforts of Wilson and Phillips in going clear inside the time and ensured the home favourites remained firmly on course for a possible gold medal.

The Sussex-based rider was just over five seconds inside the time as Miners Frolic continued his comeback from serious illness.

The horse nearly died last year after contracting colitis, and he only qualified for London in March when Cook took him to an event in Ireland.

As a protracted day neared its conclusion, Britain continued to pile the pressure on as Cook moved third individually.

And it meant Germany's reigning world champion Michael Jung needed to produce one of his finest displays to potentially prevent Britain from moving into gold medal position overnight.

PA