By Pritha Sarkar

RIO DE JANEIRO (Reuters) - Simone Biles showed the world why she is an Olympic champion-in-waiting as she and her American teammates blew away the opposition by almost 10 points in women's gymnastics qualifying at the Rio Games on Sunday.

The quintet of Biles, 2012 all around champion Gabby Douglas, Aly Raisman, Laurie Hernandez and Madison Kocian produced the kind of command performance that has made the Americans an unbeatable force since 2011 as they racked up a total of 185.238 points.

While rivals China, Russia and Britain fell and stumbled their way through qualifying, the only blips for the Americans was when Douglas stepped out of bounds during the floor exercise and Raisman flapped her arms about to save herself falling off the beam following a big wobble.

They were such a class act with their soaring somersaults and explosive tumbles that Biles, Raisman and Douglas were the top three all around performers on Sunday.

But the quality within her own team meant that Douglas lost her chance to become the first woman since Czech Vera Caslavska in 1968 to win back-to-back Olympic all around titles as competition rules state each country can field only two gymnasts in individual finals.

Her total of 60.131 was just 0.476 of a point adrift of Raisman, who along with Biles made it to the all around final.

"I hate the two per country rule, I think it’s really hard because I think all five of us could make the all around final," said Raisman.

"It is heart-breaking."

While a dejected Douglas was left to dwell on a missed opportunity, Biles was flying high. She became the only woman to breach the 16-point barrier on Sunday and was on target to become the first female gymnast to win five golds at a single Olympics by topping the floor, vault, beam and all around standings.

Though no-one could come close to Biles, Britain's Ellie Downie proved herself "a fighter" when she carried on after a horrific landing on her neck.

There was an audible gasp in the arena when Downie's tumbling run on the floor exercise ended with her clutching her neck after she suffered what she called "a crunch in my neck".

Despite being helped out of the arena to get medical attention, the 17-year-old was back in action 15 minutes later and executed two soaring vaults to provisionally leave Britain fourth in qualifying.

"It was very scary and a shock to the system. Ellie's a fighter for coming back," summed up elder sister Becky, who earned the team's highest score of 15.233 on the asymmetric bars.

China's hopes of regaining the team title they relinquished to the U.S. in 2012 may end up being a mere pipe dream after a series of shaky performances left them a distant second with 175.279 points.

Unless they iron out the wobbles and flaws that marred Sunday's routines, China could be left off the team podium for the second Games running.

Nerves appeared to get the better of 16-year-old Olympic debutante Mao Yi and teammate Shang Chunsong.

Mao landed out of bounds following her first tumbling run, put a hand down and then rolled on to her knee after the second tumbling combination and botched her landing on the third. A score of 11.700 reflected her flop show.

Shang's vault also went awry, drawing 12.766.

Russia, the 2012 silver medalists, stood third with a total of 174.620.

Uzbek Oksana Chusovitina's gamble to keep going at the age of 41 almost certainly paid off as the oldest ever gymnast to compete at an Olympics looked set to make the eight-woman vault final with an average score of 14.999.

(Reporting by Pritha Sarkar; Editing by Rex Gowar and Andrew Hay)