TOKYO -- It didn’t even look like he was working. With the languid ease of a man going on an evening stroll, 21-year-old Roki Sasaki rocked back and threw triple-digit heat on repeat. The right-hander topped 100 mph a remarkable 21 times -- in just 66 pitches -- during Japan’s 10-2 victory over the Czech Republic on Saturday, all but clinching a spot in the quarterfinals.

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And yet, this remarkable young pitcher who nearly threw back-to-back perfect games in Nippon Professional Baseball, found his team down one to the Czech Republic at the end of the first inning thanks to a Marek Chlup double and a throwing error from shortstop Takumu Nakano.

When you’re the Czech Republic, the tournament’s most beloved fan favorite, that’s just what happens.

Japan officially clinched a berth in the quarterfinals later via Korea's 7-3 victory over the Czech Republic. Japan next faces Australia on Sunday (6 a.m. ET, FS1) and hopes to complete a perfect 4-0 run through the first round.

While Sasaki was throwing 100-mph pellets that zipped by with a blur, the Czech Republic countered with Ondrej Satoria, an electrician by trade. Nicknaming his changeup “The Worker” -- because his changeup does all the work for him -- Satoria managed to keep Japan’s hitters confused and off balance, wracking up four strikeouts despite throwing a fastball that never touched 80 mph.

That included strikeouts of Lars Nootbaar and Shohei Ohtani -- even getting Ohtani to stumble and lose his helmet.

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"What I'll remember is Satoria's first inning," manager Pavel Chadim said. "It was strikeout, strikeout and ground ball to first. Then Shohei struck out in his second time up. ... Three strikeouts from three of the best hitters from Japan in the lineup. I think this moment was big. Another big moment was double from Marek. A big moment was the RBI -- I know it was an error, but this first run against Japan and leading 1-0 against the best team? This is the moment [I'll remember]."

Unfortunately for the 200 or so cheering Czech fans who were in attendance following Friday’s remarkable comeback victory against China, there’s only so long that Japan’s fearsome bats will stay quiet.

Japan put up three runs in the bottom of the third, tacked on four more in the fourth and methodically grinded the game away, showing why this team is a favorite to win the whole tournament. Kensuke Kondoh continued his hot hitting with two more hits, and Ohtani doubled and even stole third base.

“It is such a dream come true to face the Japan team for the Czech Republic. I can't believe that we are playing tonight against Japan,” Chadim said before the game. “We don't know the result yet, but all I can promise to you is play hard, never give up and I hope we’ll play until the ninth inning.”

Though the Czech Republic lost, afterward Chadim was just as complimentary.

"Tonight's experience in front of the packed audience, this is probable the most joyful moment throughout their playing career," Chadim said. "My players felt so much joy playing baseball from the fans.

"I think Japan is the best team in the world in baseball. Japan has the best fans in the world, and the best player ever was Ichiro Suzuki."

The feeling was reciprocated by Japan manager Hideki Kuriyama.

"We felt all the players are eager to improve their skills, and they play hard, and so we felt a joy playing against them," Kuriyama said. "We recognized something that we'll never forget through the Czech Republic's attitude."

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While the victory clinched Japan’s place in the quarterfinals, the game had even more meaning for Sasaki. The game was played on the 12th anniversary of the 3/11 disaster, when the Tōhoku earthquake and tsunami claimed the lives of 19,759 people, including Sasaki’s father and grandfather.

“Twelve years ago, we had a 3/11 earthquake,” Kuriyama said before the game. A reporter at the time of the disaster, Kuriyama saw much of the devastation firsthand. “I understand a lot of Japanese people are still suffering from it. There’s not much we can do, but throughout our baseball game, I hope the Japanese people forget about the 3/11 disaster and I want for everyone to have joy. I hope that the baseball gods are wishing Roki Sasaki well.”