Kohei Uchimura offered a reminder of the skillset that has brought him three Olympic gold medals before the unimaginable happened, delivering a major jolt to hosts Japan.

The veteran national sporting hero only entered the horizontal bar event at Tokyo 2020 and hoped to sign off his Games career with a golden flourish.

But on the first full day of competition at the Ariake Gymnastics Centre, Uchimura lost his grip after a mesmerising start to his routine, and fell down onto the crash mat.

His hopes not only of gold, but of a medal of any colour, were over. Uchimura was also certain to miss out on the final, and must have known that as he climbed back onto the bar, performing and dismounting flawlessly second time around.

Uchimura won all-around gold at London 2012 and Rio 2016, also taking team gold in Brazil five years ago. He also won two silver medals both in Beijing and London.

This time, his score of 13.866 put Uchimura way out of contention, and the 32-year-old accepted his fate.

"I couldn't perform what I have practised," he said. "That's how I simply think. In the last three Olympic Games I could perform what I practised. But I couldn't do that at these Olympics.

"I hit my peak already. It has been so tough to get selected as a national team member. That itself was already really tough. So maybe that's why."

Asked whether that would be his swansong, Uchimura asked for time to consider his future. Retirement is certainly an option.

"Let me think about it when I go back to the accommodation," he said. "But I have experienced the bottom of the bottom when I wasn't doing well. So I am not as disappointed as I expected."

Uchimura's exit was a blow to the Japan team, but there may be many highs still to come in the gymnastics arena.

That was Uchimura's view, after he took time to observe and was struck by the reality that Japanese gymnastics is moving into a new era, beyond his time as talisman.

"They are a really strong team," he said. "After I finished the horizontal bar and came back to the arena to watch, I saw them sorting out their problems on their own. I felt I wasn't needed anymore."