RIO DE JANEIRO (AP) — Russian gymnastics star Aliya Mustafina said in the weeks leading up to the Olympics the star-laden U.S. team is pretty much unstoppable.

Given a chance following Olympic preliminaries on Sunday to take it back, Mustafina instead doubled down. Considering the way the two teams most likely to challenge the U.S. performed during early qualifying, it's hard to blame her.

"It's going to be really difficult to compete against the American team," Mustafina said through a translator. "They are unbeatable at the moment."

China and Russia both struggled at times on Sunday, beset by mistakes they can't afford to make if they want to make the team finals on Tuesday anything more than a coronation.

While the Chinese led through two subdivisions after posting a score of 175.279 — just ahead of Russia's 174.620 — they didn't do much to strike fear in the Americans as they prepared to take the floor later Sunday afternoon.

"We need to fight," said Mustafina, the 2010 world champion. "We need to do our best and see what happens, but it's going to be quite difficult."

It wasn't a disaster exactly, it just wasn't crisp. While Mustafina put on a near flawless display on uneven bars while throwing up 15.833, she also plopped off the balance beam. Daria Spiridonova's 15.683 nearly matched Mustafina but she was all over the place on floor.

Mustafina chalked up Russia's problems to jitters, ones she believes will evaporate by the finals.

"It's hard in the first day because you don't really know what atmosphere is going to be, how the environment is going to be, so it is really, really difficult the first day to overcome all those feelings," Mustafina said.

Though the Russian team has been dogged by doping suspensions, there were no sanctions against the gymnastics program — which did not have an athlete mentioned in a scathing pre-Olympic report. Mustafina called the chaos surrounding the Russian team's status before arriving in Rio "inconvenient" but doesn't believe it became a distraction.

"I'm not really one of those who sits and browses the web all the time so I really didn't take much notice of it and didn't think about it very much, either," she said.

China has its own set of issues. Even veteran Shang Chunsong wasn't immune. She botched her vault and put up an all-around total of 56.532. While she will easily advance to the all-around final — where the scores are reset — she admitted she was at about 70 percent after missing a chunk of training before the games because of illness.

Oksana Chusovitina made a strong bid to extend her stay at a seventh Olympics. The 41-year-old from Uzbekistan averaged 14.999 on her two vaults, likely good enough to make it to the event finals. Though she's a generation older than most of her competitors, Chusovitina doesn't feel like it when she's on the floor.

"Well, when I compete on the podium, if they gave a few more marks for the age, it would have been great," she said. "Otherwise, well, we're all equal and we just have to compete against each other as equals."

Chusovitina originally planned to finally retire after London four years ago, only to change her mind. She made no proclamations about the future on Sunday. When her 17-year-old son Alisher asked her recently if this was her final go-around, she said simply "wait and see."

The U.S. team, led by three-time world champion Simone Biles and defending Olympic champion Gabby Douglas, were scheduled to compete later Sunday.