Japan hardly looked like a dominant force as it slogged through preliminary qualifying on Saturday morning.

The men were bedeviled by uncharacteristic mistakes all over the place — from defending champion Kohei Uchimura falling off the high bar to world floor exercise champion Kenzo Shirai stepping out of bounds during his set.

Ryohei Kato competes on the parallel bars (Getty Images/Alex Livesey)

While Japan is hardly in danger of missing Monday's eight-team final after posting a score of 269.294, they know they need to be sharper — much sharper — by Monday evening.

The Japanese ended rival China's long run at the top when they surged to gold at the 2015 world championships. Eyeing a chance to bookend that breakthrough with a triumph in Rio de Janeiro, they instead looked a bit overcome by the stage.

"We try to perform like the world championships," Uchimura said. "But we know this is the Olympic Games and this makes us stressed out."

Even the typically poised Uchimura wasn't immune. Looking for a gold medal to bookend the one he captured in London, he went sailing off the high bar — an event where he is the reigning world champion — and smacked onto the mat in frustration. The miscue means he'll miss the event final, though his all-around score of 90.498 was tops during his subdivision and he's assured of a spot in the all-around final next Wednesday.

"I don't think the mistake on the high bar was a bad thing, because it makes me recognize and focus that I am performing in the Olympic Games," Uchimura said.

While Japan struggled, host Brazil soared. Buoyed by a fervent home crowd that roared with every hit routine, the Brazilians were a close second to the Japanese and are a threat to make the Olympic team final for the first time.

The highlight came during three-time Olympic veteran Diego Hypolito's floor exercise. After falling in the 2008 floor final and failing to make the event final in 2012 after a similar mistake, tears streamed down the 30-year-old Brazilian's face after posting a 15.5.

 Diego Hypolito, Francisco Barretto Junior, Arthur Mariano, Sergio Sasaki and Arthur Zanetti celebrate qualification on Day 1 of the Rio 2016 (Getty Images/Alex Livesey)

"This was important for Brazil, it was about the team," Hypolito said. "I've been to three Olympics. This is something we've thought about for a long time. To perform like this, it's a dream."

Britain and the United States are scheduled to qualify in subdivision 2, with China and Russia competing in the final session on Saturday night.

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