The reigning world champion on the event will anchor the heavy gold medal favorites as they begin their quest for their first Olympic title since the 1996 Atlanta Games.
The 16-year-old Maroney aggravated an injury to her right big toe during practice last week but looked fine during podium training Thursday, drilling a series of difficult Amanar vaults that give the U.S. a decided advantage over the rest of the 12-team field.
World all-around champion Jordyn Wieber, trials winner Gabby Douglas and team captain Aly Raisman will do all four events for the U.S., with Kyla Ross replacing Maroney on uneven bars, balance beam and floor exercise.
The U.S. dominated at worlds in Tokyo last fall, winning the team crown by a whopping four points, a blowout that could be repeated at the O2 Arena over the next week.
Opposing countries have been so curious about what the Americans are doing that they have "accidentally" wandered by the team's practice sessions.
They needn't have been so secretive. Maroney and company were only too glad to put on a display during podium training, working like a pink-clad machine, particularly on vault.
The U.S. is the only country in the field that has four competitors who can do the Amanar, named after 1996 vault champion Simona Amanar. It is arguably the toughest vault being done in competition, and the ability of the U.S. to land the high-scoring skill four times gives it a significant point cushion that will be difficult for opposing countries to overcome.
Each team enters four athletes per event, with the top three scores counting.
The top eight teams at the end of the night make the finals on Tuesday, which moves to the "three-up, three-count" format.
The stiffest test for the U.S. is expected to come from defending Olympic champion China, Russia and a resurgent Romanian squad that won the European championships handily this spring.
Still, there's little doubt the U.S. is the team to catch, particularly with Maroney healthy enough to do her thing.
Eyebrows were raised just before the games when she was held out for much of training, spending time behind a small protective wall with her feet hidden from view.
Turns out she'd accidentally kicked a beam during practice shortly after the U.S. arrived in London, causing her big toe, which she broke at a competition in Chicago in May, to start throbbing again.
The only real treatment is time off. She won't get any until after the games and will grit her way through the vault with her big toe and second toe taped together.
She'll spend the rest of Sunday watching her teammates go to work. The biggest subplot will be the budding rivalry between Wieber and Douglas.
Wieber has steamrolled the competition for the past three years but was upended by the sprightly Douglas at trials. Both have stressed they're focused on the team gold, but the qualification round will mark the start of what could be a gripping week in which the U.S. tries to repeat the 1-2 all-around finish produced four years ago by Nastia Liukin and Shawn Johnson.
If Douglas or Wieber falters, Raisman is more than capable of bumping one out of the all-around. The top 24 individual finishers move on to the finals Thursday, but Olympic rules allow only two athletes from any country to advance, meaning at least one of the three Americans will watch from the stands in a sweatsuit.
It's that kind of depth that has made the U.S. a prohibitive favorite. Wieber, Douglas, Maroney and Raisman were all part of the world championship team that crushed the field in Tokyo. The 15-year-old Ross has fit right in, her elegant lines a marked contrast in style to some of her more muscled teammates.
Ross has hardly been intimidated by the stage, soaring at trials last month to finish second on bars behind Douglas. She was sharp in training on Friday, earning praise from team coordinator Martha Karolyi after a series of no-wobble beam routines.
A repeat performance Sunday should set the stage for the biggest night in U.S. gymnastics in 16 years.
