LONDON >> American McKayla Maroney’s rare mistake cost her a gold medal on vault that was all but hers. Maroney appeared to land her second vault on the backs of her heels. Her feet slid out from under her, and she plopped on the mat, a look of shock crossing her face.

“I already knew that I pretty much only had the silver medal. I really didn’t deserve to win a gold medal if I fall on my butt,” Maroney said. “I was still happy with a silver, but it’s still just sad.”

Sandra Izbasa of Romania won the gold.

Maroney was considered all but a lock for the gold medal, which would have given the U.S. women three in the first three gymnastics events. She won her world title last year by almost a half-point, and topped qualifying here by a similar margin. She was so impressive in Tuesday night’s team final that U.S. coach John Geddert suggested they rename her vault “The Maroney.”

“Man, that thing is beast!” all-around champion Gabby Douglas said earlier Sunday. “How she gets so high, I’m so amazed. When she does it at camp, the table literally shakes.”

Her first vault was the Amanar — a roundoff onto the takeoff board, back handspring onto the table and 2.5 twisting somersaults before landing — and she did it better than the woman for whom it’s named. She got such great height off the table the folks in the first few rows had to look up to see her, and her form was perfect in the air, legs pencil-straight, body tightly coiled.

She took a hop on her landing, and came down out of bounds. But even with that 0.3 deduction, she still scored 15.866, including a whopping 9.666 for execution.

Another vault like that, and the gold was hers.

But she appeared to land the second one on the back of her heels. Her feet slid forward and she dropped to the mat with a loud “plop!” The crowd gasped, and Maroney looked stunned. She’s as consistent as a Swiss watch on vault, never making errors in training or in competition.

She scored just a 14.3, giving her an average of 15.083. Coach Arthur Akopyan tried to console her, but Maroney simply stared straight ahead, knowing her chance to add an individual gold to the one she won with the Fierce Five was gone.

“I still walked out of the Olympics with a silver medal, so I’m really happy,” Maroney said.

Later, a tiebreak cost Louis Smith once again.

Four years after he dropped from second to bronze in pommel horse, a tiebreak got the British gymnast again, giving him silver instead of gold.

He and Hungary’s Krisztian Berki finished with identical 16.066 scores, but Berki got the gold because his execution score of 9.166 was .10 points better. With the Duchess of Cambridge, the former Kate Middleton, sitting in the front row, just a few feet away from him, Smith stared at the scoreboard with a look of astonishment.

Still, it wasn’t a bad day for the British. Four years after Smith gave them their first individual gymnastics medal in a century, they got another — two, actually, with Max Whitlock taking the bronze. As the two left the arena, Smith flashed a “V for victory” sign at a TV camera.

Earlier Sunday, Smith’s bronze on pommel horse in Beijing was a proud moment for the British, who weren’t even an afterthought in gymnastics a decade ago, and it gave him the kind of celebrity status usually reserved for soccer stars. He did the rounds of talk shows, and showed up in ads for everything from fast food to clothes to cars. He even got to meet the Queen.

Expectations were massive — Middleton doesn’t show up at just any event — and Smith didn’t disappoint. Most gymnasts simply try to get through their pommel horse routines unscathed, looking as if they’re trying to wrestle a bucking bronco to the ground. But Smith is silky smooth.

His work on one pommel, so difficult because of the focus and consistency it takes, is exquisite. His lower body looked as if it was on a swivel as he swings his legs in perfect circles. The only sound in the arena was the slap, slap, slap of his hands on the horse.

He picked up speed as he began to move across the apparatus, looking like a small plane readying to take off. But his control never faltered, and the crowd began cheering as he pushed into his dismount, pirouetting around the horse with his legs spread in a wide “V.” Ever the showman, he picked one of his hands up for an added flourish, delighting the audience.

When his score flashed, a brief look of confusion crossed Smith’s face, followed by one of resignation. He quickly made his way over to Berki, his longtime rival, and the two embraced.

Also Sunday, Zou Kai won his fifth career gold medal, defending his title on floor exercise. He already had one gold from China’s victory in the men’s team competition last week, and has three more from the Beijing Games. He’s got a chance to duplicate his Beijing three-peat on Tuesday, when he tries to defend his Olympic title on high bar.

Zou doesn’t have all-around champion Kohei Uchimura’s precision or elegance, coming in low on a couple of landings and taking a small hop on his final tumbling pass. But his routine is so packed with difficult tricks it’s a wonder he’s got the energy to walk off the podium when he finishes. His power was evident on his opening tumbling run, landing with such force the floor shook.

He knew it was good when he finished, pumping his fist as he trotted off. It was, his 15.933 putting the gold out of Uchimura’s reach and everyone else’s. All that was left was to wait out the competition and when the final gymnast finished, Zou reached in his bag for a red and gold banner that read, “Five Gold Crown Nine Provinces.”